Use this recipe to make the base of the Croquembouche. It is best made on a clear, dry day. Humidity makes the nougat sticky and difficult to work with.
Heat oven to 300 degrees. In a medium saucepan, combine the sugar and the lemon juice -- it should have the consistency of wet sand. Place over medium heat; do not stir. Clip on a candy thermometer, and continue to boil until the mixture reaches 340 degrees. Remove from heat, and immediately stir in the almonds.
Pour the mixture onto an oiled Silpat (a French nonstick baking mat) or countertop, and spread out with an oiled offset spatula. Fold the nougat over itself several times to cool slightly. While it is still warm, roll it out into a 10-inch disk with an oiled rolling pin. Lightly oil a 6-inch fluted tart pan; place on an oiled baking sheet. Cut an 8- inch circle from the nougat disk, then transfer the circle to the tart pan. Press nougat into tart pan. Transfer tart pan to oven until nougat becomes pliable, about 2 minutes. Press nougat into flutes of tart pan; cut excess from edges; set aside.
Using a ruler and a sharp knife, cut the remaining nougat into 15 one-inch equilateral triangles. If the nougat becomes too stiff, place it back on a baking sheet, and return it to the oven for a few minutes to soften. Set triangles aside to cool.