Bake a thin sponge cake or use pound cake
Let the cake cool completely
Trim the cake into even layers if needed
Spread jam, buttercream, or ganache between layers
Chill the cake until firm
Cut the cake into small squares or rectangles
Place the pieces on a wire rack over a tray
Prepare fondant, glaze, or melted chocolate for coating
Pour or spread the coating over each piece
Let excess coating drip off
Transfer the petit fours to parchment paper
Decorate with piped icing, sprinkles, nuts, or candied fruit
Let the coating set completely before serving