MAKE THE TANGZHONG:
In small saucepan, whisk together bread flour and whole milk until completely smooth with no lumps.

Cook over medium heat, stirring constantly with whisk or wooden spoon, until mixture thickens to paste consistency and reaches about 150°F (65°C), about 3-5 minutes. Kim-Joy explained: It's like doing a roux. You add it to the dough and it helps it retain a bit more moisture so they'll be extra fluffy. Watch carefully and don't let temperature exceed 150°F or starches will break down.

Transfer hot tangzhong to small bowl and let cool to room temperature, about 30 minutes. Cover surface directly with plastic wrap to prevent skin formation. This can be made 1 day ahead and refrigerated.

MAKE THE ENRICHED DOUGH:
In large bowl of stand mixer or large mixing bowl, combine bread flour, granulated sugar, instant yeast, salt, ground cardamom, and lemon zest. Whisk dry ingredients together.

Add cooled tangzhong, room temperature eggs, warm milk (110°F), and vanilla extract to dry ingredients. Using dough hook attachment, mix on low speed until combined into shaggy dough, about 2 minutes.

Increase speed to medium and knead 10-12 minutes until dough is smooth, elastic, and slightly sticky. If kneading by hand, knead on lightly floured surface 15-18 minutes. Dough should be soft and pull away from bowl sides but remain slightly tacky.

Add softened butter gradually, a few pieces at a time, kneading on medium speed until fully incorporated and dough is soft, supple, and silky, about 3-4 more minutes. Paul noted the tangzhong offered up a very delicate dough, quite soft, which is good for a Chelsea bun. Don't add extra flour even if dough seems soft - tangzhong dough is naturally softer.

Place dough in greased bowl, turning once to coat. Cover tightly with plastic wrap and let rise in warm place (75-80°F) until doubled in size, about 1.5 to 2 hours. Dough should spring back slowly when gently poked.

PREPARE THE FILLING:
While dough rises, make pistachio cardamom filling. In medium bowl, mix softened butter, packed light brown sugar, ground cardamom, lemon zest, and pistachio paste (if using) until well combined and spreadable like thick frosting.

Stir in finely chopped or ground pistachios until evenly distributed. Enhanced flavor: More cardamom and generous pistachios ensure flavors are more obvious as Paul suggested, creating bold Middle Eastern-inspired profile.

ASSEMBLE THE CHELSEA BUNS:
Line 9x13-inch baking pan with parchment paper, leaving 2-inch overhang on two opposite sides for easy removal after baking.

Punch down risen dough to deflate. Turn out onto lightly floured surface. Roll dough into rectangle approximately 12x16 inches, with long edge facing you. Try to maintain even thickness throughout.

Spread pistachio cardamom filling evenly over entire dough surface with offset spatula or back of spoon, leaving 1/2-inch clean border along top long edge. Spread filling all the way to other three edges.

Starting from bottom long edge (closest to you), roll dough tightly and evenly into log, keeping roll tight and uniform. When you reach top, pinch seam firmly to seal. Position log seam-side down.

Using unflavored dental floss or very sharp knife, cut log into 12 equal slices (about 1.5 inches each). To use floss: slide under log, cross ends over top, and pull to cut cleanly without squashing. Knife method: use gentle sawing motion.

Arrange sliced buns cut-side up in prepared pan in 3 rows of 4, spacing slightly apart. They will expand and touch during rising and baking, creating pull-apart texture.

Cover pan loosely with oiled plastic wrap (oil prevents sticking). Let rise in warm place until puffy, nearly doubled, and touching each other, 45-60 minutes. Buns should spring back slowly when gently poked.

BAKE THE CHELSEA BUNS:
Preheat oven to 350°F (175°C) during final 15 minutes of rising.

Bake 25-30 minutes until tops are golden brown and internal temperature reaches 190°F. Paul praised nice color on them and your baking is very good - proper temperature ensures beautiful golden coloring without over-browning. Don't underbake or centers will be gummy.

While buns bake, make glaze: Combine milk, granulated sugar, and butter in small saucepan. Heat over medium heat, stirring, until sugar dissolves completely and mixture is hot and smooth.

Remove buns from oven when golden. Immediately brush warm glaze generously over entire surface of hot buns using pastry brush. This creates shiny, slightly sticky surface and adds extra sweetness.

GLAZE AND ICE:
Let glazed buns cool in pan 15 minutes to set slightly. Using parchment overhang, carefully lift entire batch of connected buns onto wire rack to cool completely, about 30 minutes.

While buns cool, make lemon icing: In medium bowl, whisk together sifted powdered sugar, fresh lemon juice, and lemon extract (if using for stronger citrus as Paul noted needed to be more obvious) until smooth, thick, but still pourable. Add yellow food coloring drop by drop if desired for visual appeal.

Drizzle lemon icing over cooled buns in decorative zigzag or crosshatch pattern using spoon or transfer to piping bag for more control. Kim-Joy's artistic touch: Create pretty presentation as Paul noted they look pretty.

Immediately sprinkle chopped pistachios over wet icing so they adhere. Add candied lemon peel if using for extra citrus flavor and visual interest.

Let icing set at room temperature 15 minutes before pulling apart and serving.

UNDERSTANDING TANGZHONG:
Tangzhong is Japanese technique (also called water roux) where portion of flour is cooked with liquid to gelatinize starches. This allows dough to hold significantly more moisture, resulting in softer, fluffier bread that stays fresh longer. Kim-Joy explained it's like doing a roux - same principle used in sauce-making where flour and liquid are cooked together to thicken.

CHEF'S NOTES:
Paul Hollywood's praise preserved: I think your baking is very good and quite soft, which is good for a Chelsea bun - tangzhong technique successfully creates delicate, soft texture that makes these buns exceptional.

Flavors enhanced from original: Paul noted it's delicate and it needs to be a little more obvious with citrus in there. Enhanced version doubles lemon zest to 2 lemons in dough, increases cardamom to 1.5 teaspoons in filling, adds more pistachios and optional pistachio paste, plus lemon extract in icing for bolder, more pronounced flavors that shine through sweet dough.

Citrus confirmation: Paul asked Citrus in there as well? and noted it needed to be more obvious - enhanced lemon in both dough and icing ensures bright citrus flavor balances rich pistachio filling.

Kim-Joy's innovation celebrated: Tangzhong is Asian bread-making method that creates incredibly soft, fluffy texture that stays fresh longer than traditional methods. Perfect for enriched sweet breads like Chelsea buns.

Presentation honored: Paul noted they look pretty - Kim-Joy's artistic decorative touch through zigzag icing drizzle and pistachio topping creates beautiful presentation.

TIPS FOR SUCCESS:
Tangzhong temperature critical: Don't let it exceed 150°F or starches will break down and won't provide moisture-holding benefit. Mixture should coat spoon but still pour.

Dough texture should be soft and slightly sticky: Resist urge to add extra flour. Tangzhong dough is naturally softer than traditional dough but creates superior texture.

Cutting technique matters: Use unflavored dental floss to cut rolls cleanly without squashing delicate dough and losing swirl definition.

Flavor intensity important: Don't skimp on cardamom, pistachios, or lemon - these flavors need to be bold enough to shine through sweet enriched dough as Paul noted.

MAKE-AHEAD TIPS:
Tangzhong can be made 1 day ahead and refrigerated in airtight container. Bring to room temperature before using or it will cool other ingredients and slow yeast activity.

Dough can be made through first rise, punched down, covered tightly, and refrigerated overnight. Let come to room temperature (about 1 hour) before rolling out.

Assembled unbaked buns can be covered and refrigerated overnight. Let rise at room temperature 1 hour before baking, or bake cold adding 5 minutes to time.

Baked unglazed buns freeze well wrapped tightly for 1 month. Thaw, warm gently, then glaze and ice.

VARIATIONS:
Substitute rose water for lemon in icing for Persian-inspired version with floral notes.

Add dried edible rose petals to pistachio filling for romantic Middle Eastern touch.

Use orange zest instead of lemon for different citrus profile that pairs beautifully with cardamom.

Add white chocolate chips to filling for extra sweetness and creamy pockets.