Sift powdered sugar and almond flour together into a bowl or onto a large plate. Discard any coarse bits.

In a large bowl of a stand mixer, beat egg whites on medium speed until foamy. Add cream of tartar and mix to combine. Gradually add granulated sugar and beat until stiff, glossy peaks form, about 4-5 minutes.

Add vanilla extract and gel food coloring if using and beat just to combine.

Gently fold in the sifted almond mixture in thirds, using a spatula. Mix until the batter flows in thick ribbons and forms a figure-eight without breaking.

Transfer batter to a piping bag fitted with a round tip. Pipe 1-inch circles onto the prepared baking sheets, spacing them 1 inch apart. Tap the baking sheets firmly on the counter to release air bubbles. You can pop small air bubbles that are forming on the surface with a toothpick. Let macarons rest at room temperature for about 1 hour or until the tops are dry to the touch.

Preheat oven to 300°F. Bake one tray at a time for 14-16 minutes. Shells should rise with feet and not crack. Cool completely before removing from the parchment paper.

For the filling, beat butter until creamy. Add powdered sugar gradually, then vanilla and cream. Beat until fluffy.

Pipe a small amount of filling onto the flat side of one shell and sandwich with another.

For the best texture, refrigerate assembled macarons for 24 hours, then bring to room temperature before serving.