Preheat your oven to 350°F (175°C) and grease a square pan. Combine almond flour, eggs, granulated sugar, butter, and vanilla extract to make the almond cake batter. Pour into the pan and bake for 25–30 minutes until a toothpick comes out clean. Cool completely on a wire rack before slicing.

While the cake cools, prepare the buttercream by beating unsalted butter and powdered sugar until fluffy, then gradually adding milk until smooth. Spread a thin layer over each cooled cake piece.

Melt white chocolate and corn syrup together until smooth. Dip each buttercream-coated cake piece into the white glaze until fully covered. Let excess glaze drip off and place on a wire rack to set.

Press almond slices onto the glaze-coated petit fours for decoration. Ensure the glaze is tacky enough to hold the almonds.

Allow the petit fours to set at room temperature for about 30 minutes. For a firmer finish, refrigerate for an additional 15 minutes before serving.