Paris-Brest

Spread the toasted hazelnuts on a silicone mat. In a clean, dry saucepan, heat the caster sugar over medium heat without stirring until the edges begin to melt. Gently swirl the pan and continue until all the sugar is a deep amber caramel — the color of a copper penny. Immediately pour over the hazelnuts in a thin sheet. Let set hard at room temperature, about 20 minutes. Break into chunks and process in a food processor for 4–6 minutes, scraping down often, until it transforms from crumble to paste. The oils in the nuts will release and the paste will become pourable and glossy.

Combine water, butter, and salt in a heavy saucepan. Bring to a full rolling boil — every bit of the butter must be melted before the boil, or the ratio is thrown off. Remove from heat and add all the flour at once. Stir vigorously with a wooden spoon until a cohesive ball forms and pulls away cleanly from the sides. Return to medium heat and cook the panade, stirring constantly, for 2 minutes to dry it out. The dough will leave a thin film on the pan bottom.

Beat the panade with a paddle attachment on medium speed for 1 minute to cool slightly and release steam. Add the beaten eggs in four additions, allowing each to fully incorporate before adding the next. The paste will look broken and curdled after each addition — keep beating and it will come together. Stop when the paste falls from the paddle in a slow, thick V-shape (the 'beak test').

Preheat oven to 200 C (390 F). Trace a 22 cm circle on parchment. Pipe the choux paste in a double ring — one ring on the traced line, a second ring just inside it, then a third ring on top of the join. This creates a wide, stable ring that can be split cleanly. Brush with egg wash and sprinkle with sliced almonds. Bake for 35–40 minutes without opening the oven until deeply golden. Crack the oven door with a wooden spoon and bake 5 more minutes to dry the interior.

Make a pastry cream: whisk the yolks with 50g sugar and 20g cornstarch until pale. Bring milk to a simmer, pour over the yolks while whisking, return to the pan, and cook until thick and bubbling. Whisk in 55g room-temperature butter and 80g praline paste. Chill completely. Whip the cold cream to soft peaks. Whip the cold pastry cream until smooth and silky, then fold the whipped cream in thirds into the praline cream until just combined.

Use a serrated knife to split the choux ring horizontally, cutting through the widest point — aim for a 40/60 split, with the larger piece on the bottom. Pipe the mousseline in generous, tall rosettes along the entire interior of the bottom ring, mounding it higher than the ring's edge. Set the top ring gently over the cream. Dust with powdered sugar and serve within 2 hours.