Sift together powdered sugar and almond flour into a large bowl. Discard any large pieces that remain in the sifter.

In a separate bowl, beat egg whites with cream of tartar until foamy. Gradually add granulated sugar and vanilla, beating until stiff peaks form. Add food coloring if desired.

Gently fold the dry ingredients into the meringue in three additions. Mix until the batter flows like lava and makes a ribbon when lifted.

Transfer batter to a piping bag fitted with a round tip. Pipe 1-inch circles onto parchment-lined baking sheets. Tap the sheets firmly to release air bubbles.

Let the macarons rest at room temperature for 30-60 minutes until a skin forms. They should not be sticky to the touch.

Preheat oven to 300°F (150°C). Bake for 12-15 minutes, rotating halfway. Let cool completely before removing from sheets.

For the ganache: Heat cream until steaming, pour over chopped chocolate, let sit for 2 minutes, then stir until smooth. Chill until thickened.

Pipe ganache onto half the shells and sandwich with remaining shells. Refrigerate for 24 hours for best texture.