Preheat oven to 350°F (175°C). Grease a baking pan. In a mixing bowl, combine almond flour, powdered sugar, room temperature eggs, softened butter, and vanilla extract. Beat until smooth, about 3–5 minutes. Pour batter into pan and bake for 25–30 minutes until golden.

Once baked, cool in the pan for 10 minutes. Transfer to wire rack to cool completely for about 30 minutes. Slice into uniform pieces.

In a separate bowl, whip softened butter for 2 minutes until fluffy. Gradually add powdered sugar and a splash of milk, mixing until smooth and creamy, about 4-5 minutes.

Spread buttercream between two pieces of almond cake. Continue layering until all pieces are stacked. Smooth any excess buttercream with a spatula.

Melt white chocolate or prepare fondant until smooth. Dip each petit four in the melted chocolate or roll in fondant, ensuring coverage. Allow excess to drip off and space apart on a wire rack.

Press almond slices onto the top of each petit four before the coating sets.

Place petit fours in the refrigerator for 30 minutes to an hour to set the coating.