1. Preheat your oven to 300°F (150°C). Line a baking sheet with parchment paper.
2. Sift the almond flour and powdered sugar together into a bowl. Set aside.
3. In a separate bowl, beat the egg whites until foamy. Gradually add the granulated sugar and continue to beat until stiff peaks form.
4. Add the vanilla extract and food coloring (if using) to the egg whites and mix until combined.
5. Gently fold the almond flour mixture into the egg whites until the batter flows like lava.
6. Transfer the batter to a piping bag fitted with a round tip. Pipe small circles onto the prepared baking sheet.
7. Tap the baking sheet on the counter to release any air bubbles. Let the macarons sit at room temperature for 30-60 minutes until a skin forms on the surface.
8. Bake for 15-18 minutes, or until the macarons have risen and set. Let cool completely before removing from the baking sheet.
9. For the filling, beat the butter until creamy. Gradually add the powdered sugar and vanilla extract, and beat until smooth.
10. Pipe the filling onto the flat side of a macaron shell and sandwich with another shell. Repeat with remaining macarons.