1Preheat oven to 350 degrees F (175 degrees C). Spread almonds onto a baking sheet. Line a 9x13-inch baking dish with parchment paper.
2Bake almonds in the preheated oven until toasted and fragrant, 7 to 8 minutes. Chop almonds.
3Beat 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.
4Press dough evenly into the prepared baking dish. Sprinkle remaining almonds over dough, pressing lightly.
5Bake 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.
You can alternately set oven to 325 degrees F (165 degrees C) for pure convect, if desired. Bake brittle for 18 minutes instead of 20 minutes.
I used Kitchen Aid(R) mixer when adding the flour and lemon zest to butter mixture.
1 cup sliced almonds
3/4 cup butter
3/4 cup white sugar
1 teaspoon vanilla extract
1 teaspoon lemon extract
1/8 teaspoon salt
1 1/2 cups all-purpose flour
1 1/2 teaspoons finely grated lemon zest
1 tablespoon sifted confectioners' sugar, or as needed (optional)