Prepare the dry ingredients: Sift together the powdered sugar and almond flour in a large bowl to remove lumps and create a fine mixture.

Make the meringue: In a separate bowl, beat the egg whites until foamy. Gradually add the cream of tartar and granulated sugar. Continue beating until stiff peaks form (approximately 5 minutes).

Combine the meringue with the dry ingredients: Gently fold the sifted dry ingredients into the meringue in batches. If using food coloring, add it during this step. Mix until the batter flows like lava, not too runny.

Pipe the macarons: Line a baking sheet with parchment paper. Using a piping bag fitted with a round tip, pipe 1-inch circles of batter onto the sheet, spaced about 2 inches apart.

Let the macarons rest: Allow the piped macarons to sit for 30-60 minutes until a skin forms on the surface, which should not be sticky when lightly touched.

Bake the macarons: Preheat the oven to 300°F (150°C). Bake the macarons for 12-15 minutes, rotating halfway through. The shells should be crisp on the outside with a chewy interior.

Make the filling: Beat together the softened butter, powdered sugar, and vanilla extract until light and fluffy.

Assemble the macarons: Once the shells are completely cooled, spread or pipe a small amount of filling onto the flat side of one macaron shell. Sandwich it with another shell.

Chill the macarons: For best results, refrigerate the assembled macarons for 24 hours to let the flavors meld.