How to Make It
Preheat oven to 350°F.
In an electric mixer fitted with whisk attachment, beat egg whites on medium until foamy, about 1 to 2 minutes. Increase speed to high, and 1 tablespoon at a time, add 1/2 cup granulated sugar; beat until stiff peaks form, about 3 to 5 minutes. Transfer egg whites to a separate bowl.
Beat egg yolks and remaining 1/2 cup granulated sugar in an electric mixer fitted with paddle attachment on medium until pale and creamy, about 2 minutes. Add zest, juice, salt, and extract; beat until combined. Fold in almond flour. Spoon one-third of egg whites into yolk mixture; gently fold until combined. Add remaining egg whites; gently fold until combined. Spoon mixture into a 9-inch springform pan coated with cooking spray. Sprinkle almonds around outside edge.
Bake at 350°F until cake springs back when lightly touched in the middle, 35 to 40 minutes. Run a knife around pan edge. Cool cake in pan on a wire rack 10 minutes; remove pan sides. Cool cake fully on wire rack. Sprinkle with powdered sugar.