Black Sesame Thai Tea Cake

STEP 1: MAKE THE BLACK SESAME SPONGE
Preheat the oven to 350°F (175°C) and line a Swiss roll tin with parchment paper. Whisk the egg yolks with half the sugar until pale and ribboning, then whisk in the oil, black sesame paste, and vanilla. Sift in the flour, black sesame powder, and salt and fold to a smooth, dark batter. In a clean bowl, whisk the egg whites to soft peaks, add the remaining sugar a spoonful at a time, and whisk to firm, glossy peaks. Fold the whites into the sesame base in three additions, keeping as much air as possible.

STEP 2: BAKE AND ROLL
Spread the batter evenly into the tin and bake for 10–12 minutes, until just springy. Turn out immediately onto a clean tea towel dusted with a little extra black sesame powder, peel off the parchment, and roll the warm sponge up in the towel from the short end. Leave to cool rolled — this trains the sponge so it will re-roll around the buttercream without cracking, the key to a clean vertical layer.

STEP 3: STEEP AND BUILD THE THAI TEA BUTTERCREAM
Warm the cream with the Thai tea leaves until hot, then leave to infuse for 10–15 minutes and strain, pressing the leaves; cool the tea-infused cream completely. Make a Swiss meringue: whisk the egg whites and sugar over a bain-marie to 160°F (70°C) and until the sugar has dissolved, then whip to a stiff, cool, glossy meringue. With the mixer running, add the softened butter a cube at a time until smooth and silky (if it splits, keep whisking — it will come together). Beat in the cooled Thai tea cream and salt. The sugar here is held at the reduced level so the whole cake lands balanced against the sponge.

STEP 4: FILL AND RE-ROLL
Gently unroll the cooled sponge. Spread an even layer of Thai tea buttercream right to the edges, then re-roll the sponge tightly without the towel. To build the vertical layer cake, slice the filled roll into pinwheels and stand them on a board, or cut the roll into strips and coil them upright into a tall round — either way the spiral of sponge and buttercream now runs vertically through the cake. Chill briefly to firm, then coat the outside with the remaining buttercream, smoothing with a bench scraper.

STEP 5: SESAME CARAMEL SHARDS
Cook the sugar and water to a deep amber caramel, stir in the toasted black & white sesame seeds, and pour onto a silicone mat or lightly oiled tray. Let it set hard, then crack into jagged shards. Work fast — the caramel sets quickly once off the heat, so have your tray ready.

STEP 6: DARK CHOCOLATE DRIP & FINISH
Warm the cream and pour over the chopped dark chocolate; stir to a smooth, pourable ganache and let it cool until just thick enough to drip without running off the plate. Spoon it asymmetrically over one side of the chilled cake so it falls in uneven drips down a single edge. Arrange the sesame caramel shards around the top edge so they stand up like a crown. Chill 15–20 minutes to set before slicing — a hot, dry knife gives the cleanest reveal of the vertical spiral.