📋 Instructions

1. 1Toast and grind the pecans — Heat the oven to 350F (175C). Spread the pecan halves on a sheet pan and toast for 8 to 10 minutes, until deeply fragrant and one shade darker; let cool completely. Pulse with 1/2 cup of the powdered sugar in a food processor until finely ground, about 10 short pulses, stopping before it turns into paste.
2. 2Whip the meringue — Lower the oven to 325F (165C) and line two 8-inch pans with parchment. Beat the egg whites on medium speed until foamy, then add the granulated sugar a spoonful at a time. Whip to stiff, glossy peaks, about 4 minutes; the meringue should hold a sharp peak when you lift the beaters.
3. 3Fold and bake the dacquoise — Sift the remaining 1/2 cup powdered sugar and the ground pecans over the meringue in three additions, folding gently after each. Divide between the pans and smooth the tops. Bake for 22 to 25 minutes, until the tops spring back lightly when pressed and feel dry to the touch; cool completely in the pans.
4. 4Bloom the gelatin — Sprinkle the gelatin over 3 tablespoons cold water in a small bowl and let stand 5 minutes until spongy. Warm the milk in a saucepan over low heat until steaming but not simmering, about 120F (49C), then whisk in the bloomed gelatin until fully dissolved.
5. 5Build the mousse — Melt the white chocolate gently over a double boiler or in short microwave bursts, stirring until smooth. Whisk in the warm milk mixture and the vanilla paste, then cool to room temperature, about 10 minutes. Whip 1 1/2 cups of the cold cream to soft peaks and fold it into the chocolate base in two additions until no streaks remain.
6. 6Layer and chill — Line the sides of an 8-inch springform pan with acetate or parchment. Place one dacquoise layer in the bottom, pour over half the mousse, and smooth flat. Add the second dacquoise, press gently, then top with the remaining mousse. Cover and refrigerate at least 6 hours or overnight, until the center feels firm when pressed.
7. 7Make the mirror glaze — Soften the remaining gelatin in 2 tablespoons cold water. Warm the remaining 1/2 cup cream, the corn syrup, and 2 tablespoons water in a saucepan over medium-low heat to just steaming, about 140F (60C). Off heat, stir in the softened gelatin, then pour over finely chopped white chocolate (about 4 ounces) and whisk until glossy and smooth. Strain and cool to 90F (32C).
8. 8Glaze and garnish — Set the chilled cake on a rack over a rimmed pan and pour the glaze over the center in one steady stream, letting it cascade down the sides; tap the rack gently so it coats evenly. Chill 15 minutes to set, then crown with toasted pecan pieces just before serving.