Begin by sifting the powdered sugar and almond flour together in a large bowl twice.

In a clean mixing bowl, beat the egg whites at medium speed until foamy, then gradually add cream of tartar and granulated sugar until stiff peaks form.

Gently fold the sifted dry ingredients into the meringue, add green gel food coloring, and mix until the batter flows like lava.

Transfer the macaron batter into a piping bag and pipe tree shapes or circles onto lined baking sheets, then let rest for 30 to 60 minutes.

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

In a separate bowl, beat softened unsalted butter until light and fluffy, then gradually add powdered sugar, vanilla extract, heavy cream, and a pinch of salt.

Pipe a generous dollop of filling onto the flat side of one shell and sandwich it with another shell.

Place the assembled macarons in an airtight container and refrigerate for at least 24 hours to enhance flavors.