Make the Macaron Shells:

1. Prepare the Dry Ingredients:
   • Sift the almond flour and powdered sugar together into a bowl. Repeat 1-2 times to ensure a smooth mixture. Set aside.
2. Beat the Egg Whites:
   • In a clean, dry bowl, whisk the egg whites with an electric mixer until they form soft peaks. Gradually add the granulated sugar and continue beating until stiff peaks form. Add gel food coloring if desired, mixing gently until evenly distributed.
3. Combine Wet and Dry Ingredients:
   • Add the dry ingredients to the beaten egg whites in two additions. Gently fold the mixture with a spatula, being careful not to deflate the egg whites. Continue folding until the batter flows like lava and creates ribbons that disappear back into the batter within 10-15 seconds.
4. Pipe the Macarons:
   • Transfer the batter to a piping bag fitted with a round tip. Pipe small, even circles (about 1.5 inches in diameter) onto a parchment-lined baking sheet, spacing them 1 inch apart.
5. Rest the Shells:
   • Tap the baking sheet firmly on the counter a few times to release air bubbles. Let the macarons rest at room temperature for 30-60 minutes, or until the tops are dry to the touch.
6. Bake:
   • Preheat the oven to 300°F (150°C). Bake the macarons for 15-18 minutes, rotating the baking sheet halfway through. The macarons are done when the tops are set and they have formed “feet” at the base. Allow them to cool completely on the baking sheet.

Make the Filling:

7. Prepare the Buttercream:
   • Beat the softened butter until smooth and creamy. Gradually add powdered sugar and mix until well combined. Stir in vanilla extract and add milk as needed for a spreadable consistency.

Assemble the Macarons:

8. Fill the Macarons:
   • Pair the macaron shells by size. Pipe or spoon a small amount of filling onto the flat side of one shell, then gently sandwich with another shell.
9. Mature the Macarons:
   • Place the filled macarons in an airtight container and refrigerate for 24-48 hours to allow the flavors to meld and the texture to improve. Bring to room temperature before serving.