Sift the almond flour and powdered sugar together twice into a large bowl.

Whisk egg whites in a clean bowl until soft peaks form, then gradually add granulated sugar until stiff, glossy peaks are achieved.

Fold the dry ingredients into the meringue using the macaronage technique until the batter flows like lava and forms a continuous ribbon.

Transfer batter to a piping bag fitted with a round tip and pipe 1.5-inch circles onto parchment-lined baking sheets.

Tap the baking sheets firmly against the counter to release air bubbles and immediately top with rainbow sprinkles.

Rest the shells at room temperature for 30 to 60 minutes until a dry skin forms on the surface.

Bake at 300°F (150°C) for 15-18 minutes, then allow to cool completely before removing from the paper.

Heat heavy cream and pour over white chocolate; let sit for 2 minutes then stir until smooth.

Incorporate heat-treated cake mix and vanilla extract into the ganache, then chill until firm enough to pipe.

Pipe the cake batter ganache onto the flat side of one shell and sandwich with a second shell.