Sift together powdered sugar and almond flour twice to achieve a fine blend without lumps. In a mixing bowl, beat egg whites until foamy, then add cream of tartar and gradually incorporate granulated sugar until stiff peaks form, about 5-7 minutes.

Gently fold in a few drops of green gel food coloring until the desired shade is achieved. Sift the dry ingredients into the meringue mixture, folding gently until the batter is smooth, usually after about 30-40 folds.

Transfer the macaron batter to a piping bag fitted with a round tip and pipe out tree shapes on lined baking sheets. Tap the baking sheets against the counter to release air bubbles.

Allow piped shells to rest at room temperature for 30-60 minutes until a skin forms and they are not sticky to the touch.

Preheat the oven to 300°F (150°C). Bake for 14-16 minutes, rotating trays halfway through. Let them cool completely afterward.

Beat softened unsalted butter until fluffy, then mix in powdered sugar, heavy cream, vanilla extract, and salt until smooth. Fold in crumbled snack cakes to create the filling.

Spoon or pipe the filling onto one macaron shell and sandwich it with another shell, repeating until all are filled.

Decorate with melted white chocolate and festive toppings if desired.

Wrap in an airtight container and refrigerate for at least 24 hours for best flavor.