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

Beat the room-temperature egg whites on medium speed until foamy, then add cream of tartar and granulated sugar, and beat until stiff peaks form, about 5-7 minutes.

Gently fold in green gel food coloring and the almond flour mixture until batter is smooth.

Transfer the batter into a piping bag and pipe tree shapes or circles on a baking sheet lined with parchment paper.

Tap the baking sheet on the counter to release air bubbles and let the macaron sit for 30-60 minutes until a skin forms.

Preheat the oven to 300°F (150°C), bake macarons for 14-16 minutes, rotating halfway through.

Cool baked macarons completely on the baking sheet.

Beat softened unsalted butter until fluffy, gradually add powdered sugar, heavy cream, vanilla extract, and mix until combined. Fold in crumbled snack cakes.

Pipe filling onto one macaron shell, sandwich with another, decorate as desired.

Refrigerate assembled macarons for at least 24 hours to enhance flavors.