Raspberry White Chocolate Bars

STEP 1: BAKE THE HAZELNUT SHORTBREAD

Heat the oven to 325F (160C). Toast the blanched hazelnuts on a dry tray for 8 to 10 minutes until fragrant, then cool completely; warm nuts will oil the dough. Pulse them in a food processor with 2 tablespoons of the all-purpose flour until finely ground but short of a paste. Beat the cold unsalted butter with the confectioners' sugar until only just combined; you are not aerating it. Add the vanilla extract, then the ground hazelnuts, the remaining flour, the cornstarch and the fine sea salt, and mix only until the dough draws together. Divide the dough in half. Press one half evenly into the lined tin, dock all over with a fork and bake for 30 to 35 minutes, until the colour of pale straw and firm at the edges. Cool in the tin, line the tin again and repeat with the second half. Do not shorten the bake; the colour is what gives the biscuit its snap. Cool both slabs completely.

STEP 2: MAKE THE RASPBERRY GANACHE

Cook the fresh or frozen raspberries in a small pan over medium heat until collapsed, 6 to 8 minutes, then press through a fine sieve and discard the seeds. Return the puree to the pan and reduce it to about 1/2 cup (120 ml); it should coat a spoon heavily. This matters, because unreduced puree carries too much water into the chocolate and the ganache will not set firm enough to cut cleanly. Cool to just warm. Melt the white chocolate gently over barely simmering water, or in short bursts in the microwave, stirring, to no more than 110F (43C). Warm the heavy cream and stir it in, then add the reduced puree in three additions, emulsifying fully each time. Stir in the ground freeze-dried raspberries, the lemon juice and the fine sea salt. Cool to a thick, spreadable consistency.

STEP 3: SANDWICH AND CHILL HARD

Spread the ganache evenly over one cooled shortbread slab, right to the edges. Set the second slab on top and press down firmly and evenly with a flat tray so the sandwich is level. Refrigerate for at least 2 hours, then transfer to the freezer for 30 minutes before cutting. A hard-chilled sandwich is the first requirement for a clean-looking bar: cutting a soft slab drags ganache onto the cut faces, and coating over a smeared edge is what produces a messy finish.

STEP 4: TRIM AND CUT WITH A HOT KNIFE

Turn the frozen slab out onto a board. Dip a long thin-bladed knife in just-boiled water, wipe it dry, and trim a scant 1/4 inch (5 mm) from all four sides to give four true square edges. Wipe and re-dip the blade between every single cut. Cut into 16 bars, working in one direction only and pressing straight down rather than sawing. Return the bars to the freezer on a lined tray for 15 minutes. Square, dry-faced bars are what allow a thin coating to sit flat; ragged edges telegraph straight through it. Keep the bar size as it is, since the portion is right for how rich these bars eat.

STEP 5: TEMPER THE WHITE CHOCOLATE

Untempered white chocolate sets streaked, dull and blotchy, and on a pale surface there is nothing to hide it. Melt three-quarters of the coating chocolate to 110 to 113F (43 to 45C). Pour two-thirds of it onto a marble slab and work it with a palette knife until it cools to about 79F (26C), then return it to the remaining warm chocolate and stir; the working temperature for white chocolate is 84 to 86F (29 to 30C) and it must be held there. Alternatively use the seeding method: melt to 113F (45C), remove from the heat, stir in the reserved quarter finely chopped, and stir until it settles at 84 to 86F. Test by smearing a little on parchment: correctly tempered white chocolate sets glossy and firm within about three minutes at cool room temperature. If it is soft, streaked or matte, start again. Stir in the optional cocoa butter to loosen the flow without adding thickness.

STEP 6: ENROBE THINLY

Take the bars from the freezer a few at a time, but let them stand for 3 to 4 minutes before dipping: chocolate applied to a rock-frozen surface sets too fast and cracks or blooms. Drop each bar into the tempered chocolate, lift it out on a dipping fork, tap the fork firmly against the rim five or six times and draw it across the rim to shed the excess, then set the bar on the wire rack. That tapping is what does the work: it produces an even film with no pooled foot at the base, so neatness comes from control rather than from a thicker shell. Keep the coating thin. Let the bars set at cool room temperature, not in the refrigerator.

STEP 7: PIPE THE DRIZZLE

Pink on white does not read, because pink and white sit at almost the same lightness; the eye needs a difference in value, not just in hue. Ground freeze-dried raspberry solves both at once, driving the colour toward a deep raspberry-magenta and genuinely darkening the chocolate. Melt the 3 oz of white chocolate and temper it as in Step 5, then beat in the ground freeze-dried raspberries and the melted cocoa butter until completely smooth and a strong, saturated colour. Roll a parchment cornet, fill it, snip a very small tip, and pipe fine parallel or diagonal lines across the set bars in one confident pass each; stopping mid-line is what looks untidy. Scatter the freeze-dried raspberry pieces along the lines while they are still wet. Leave to set completely, about 20 minutes.

STEP 8: SERVE AND STORE

Serve at cool room temperature; straight from the refrigerator the ganache is stiff and the raspberry mutes. Handle the finished bars by the edges, as fingerprints show on tempered white chocolate, and wipe the base of each bar with a clean dry cloth before plating if any chocolate has crept underneath. Keep in a single layer in an airtight box at cool room temperature, 60 to 68F (16 to 20C), for up to 5 days. Do not refrigerate the finished bars: condensation on tempered white chocolate causes sugar bloom.