Preparation:

Step 1: Prepare the macaron shells

1. Sift dry ingredients: In a large bowl, sift together almond flour and powdered sugar to remove any lumps. Set aside.
2. Make the meringue: In a clean, dry mixing bowl, beat egg whites until foamy. Add a pinch of cream of tartar (optional, for stability). Gradually add granulated sugar while beating on medium-high speed. Continue to beat until stiff peaks form.
3. Add flavor and color: Gently fold in vanilla extract and a few drops of green food coloring. Mix until the color is evenly distributed.
4. Macaronage process: Carefully fold the almond flour mixture into the meringue using a silicone spatula. Fold gently, lifting from the bottom to avoid deflating the batter. The mixture should flow like lava and form a ribbon when lifted.
5. Pipe the shells: Transfer the batter into a piping bag fitted with a round tip. On parchment paper or silicone baking mats, pipe different-sized circles (small, medium, and large) to create stackable layers for the tree shape.
6. Rest the shells: Let the piped macarons sit at room temperature for 30-60 minutes until a skin forms. They should be dry to the touch.
7. Bake: Preheat the oven to 300°F (150°C). Bake the macarons for 15-18 minutes, rotating the baking sheet halfway through. Allow them to cool completely before removing from the parchment paper.

Step 2: Make the buttercream filling

1. In a mixing bowl, beat softened butter until creamy.
2. Gradually add powdered sugar, mixing well after each addition.
3. Add heavy cream, vanilla extract, and a pinch of salt. Beat until smooth and fluffy. Adjust consistency with more cream if needed.
4. Optional: Tint the buttercream with green food coloring for a cohesive look.

Step 3: Assemble the macaron trees

1. Match the shells: Pair up the macaron shells by size.
2. Fill the macarons: Pipe a layer of buttercream onto the flat side of one macaron shell. Gently press the matching shell on top to create a sandwich.
3. Stack to form trees: Start with the largest macaron pair at the base. Add a dollop of buttercream on top, then stack the medium-sized macaron pair. Repeat with the smallest pair to complete the tree shape.
4. Decorate: Use small round sprinkles as ornaments and a star-shaped sprinkle for the tree topper. Dust lightly with powdered sugar to mimic snow.