Preheat oven to 350 degrees F (175 degrees C). Spread almonds onto a baking sheet. Line a 9x13-inch baking dish with parchment paper.
Bake almonds in the preheated oven until toasted and fragrant, 7 to 8 minutes. Chop almonds.
Beat butter in a large mixing bowl with an electric mixer on medium-high speed for 30 seconds. Add white sugar, vanilla extract, lemon extract, and salt; beat until well combined, scraping sides of bowl occasionally. Stir flour, lemon zest, and 1/2 cup almonds into creamed butter mixture until dough is combined.
Press dough evenly into the prepared baking dish. Sprinkle remaining almonds over dough, pressing lightly.
Bake in the preheated oven until top is golden, about 20 minutes. Cool brittle in the dish on a wire rack. Sprinkle confectioners' sugar over brittle; break into chunks.