Preheat your oven to 300°F (150°C). Whip the aged egg whites in a clean mixing bowl until soft peaks form, about 2-3 minutes. Gradually add the granulated sugar, continuing to whip until stiff, glossy peaks form.

Sift together the almond flour and powdered sugar to eliminate lumps. Fold the sifted mixture into the whipped meringue in three additions, aiming for a smooth, shiny batter.

Transfer batter to a piping bag fitted with a round tip. Pipe even circles on a parchment-lined baking sheet, about 1.5 inches in diameter, leaving space between them. Tap the sheet to release air bubbles.

Allow the piped macarons to sit at room temperature for 30 to 60 minutes until a dry skin forms on the surface.

Bake the macarons for 15-20 minutes in the preheated oven, allowing them to rise and form a slight foot. Let cool for 5 minutes before transferring to a wire rack.

While cooling, prepare the buttercream filling by beating the butter until light and fluffy, then gradually adding the powdered sugar until creamy. Add food coloring to match theme.

Once the shells are cool, turn half of them upside down. Pipe a dollop of filling on each and sandwich with remaining shells.

Store assembled macarons in an airtight container in the refrigerator for at least 24 hours to allow flavors to meld.