Sift together the powdered sugar and almond flour in a large mixing bowl.

Beat the egg whites until foamy. Gradually add cream of tartar, then granulated sugar, beating until stiff peaks form.

Gently add green gel food coloring and fold in the sifted mixture until the batter flows like lava.

Pipe the macaron batter onto a parchment-lined baking sheet, forming tree shapes or circles.

Let the piped shells rest for 30 to 60 minutes until they form a skin.

Preheat oven to 300°F (150°C) and bake macarons for 14 to 16 minutes.

Beat the softened butter until creamy, then blend in powdered sugar, vanilla extract, heavy cream, and salt.

Pipe filling onto one macaron shell and sandwich it with another shell.

Melt white chocolate and drizzle over macarons, adding sprinkles if desired.

Refrigerate the assembled macarons for at least 24 hours before serving for best flavor.