Pulse 1 cup (120g) almond flour and 1 cup (120g) powdered sugar in a food processor for 30 seconds. Pass through a fine-mesh sieve into a large bowl, discarding coarse pieces.

Whip 3 large egg whites (100g) on medium speed until frothy. Slowly add 1/4 cup (50g) granulated sugar, increasing speed to medium-high. Whip until stiff, glossy peaks form.

Fold the sifted dry ingredients into the meringue using a silicone spatula. Press against the bowl to deflate air. Continue folding until batter flows like thick lava in a continuous figure-eight ribbon.

Pipe 1.5-inch circles onto a silicone baking mat. Tap the baking sheet firmly against the counter 4-5 times. Let rest at room temperature for 30-45 minutes until a dull, dry skin forms.

Preheat oven to 300°F (150°C). Bake on the middle rack for 13 to 15 minutes until ruffled feet form and shells don't wiggle. Cool completely on the pan.

Beat 1/2 cup (113g) softened butter on high for 5 minutes. Gradually add 1 1/2 cups (180g) powdered sugar, 1 tsp (5ml) clear vanilla, and 1/4 tsp (1ml) cake batter extract. Whip for 3 minutes until thick and creamy.

Using a small piping bag, drizzle thin red icing zig-zag stripes across half the cooled shells. Immediately scatter green sanding sugar sprinkles over the wet red icing. Let dry for 15 minutes.

Pipe a thick dollop of the creamy white buttercream onto the center of the bottom shells. Gently press the decorated top shells onto the filling. Refrigerate in an airtight container for 24 hours to mature before serving.