1. Prepare the Shells:

1. Sift dry ingredients:
   Combine almond flour and powdered sugar. Sift them together to remove any lumps for a smooth texture.
2. Make the meringue:
   In a clean bowl, whip the aged egg whites until they are frothy. Gradually add granulated sugar while continuing to whip. Beat until stiff peaks form.
3. Macaronage (folding the batter):
   Gently fold the dry ingredients into the meringue in batches using a spatula. Be careful not to overmix; the batter should flow like lava and form ribbons when lifted.
4. Pipe the shells:
   Transfer the batter to a piping bag fitted with a round tip. Pipe small circles onto a baking sheet lined with parchment paper or a silicone mat, using a template if needed to ensure consistent size.
5. Rest the shells:
   Let the piped shells rest at room temperature for 30 minutes to 1 hour, or until a skin forms on the surface. You should be able to touch them lightly without them sticking to your finger.
6. Bake:
   Preheat the oven to 300°F (150°C). Bake the shells for 12–15 minutes, rotating the baking sheet halfway through for even baking. Allow the shells to cool completely before removing them from the parchment paper or mat.

2. Prepare the Buttercream Filling:

1. Cream the butter:
   In a mixing bowl, beat the softened butter until it’s light and fluffy.
2. Add powdered sugar:
   Gradually add powdered sugar while mixing on low speed.
3. Adjust consistency:
   Add 1-2 tablespoons of heavy cream to achieve a smooth, spreadable consistency. Beat until well combined.
4. Optional flavoring:
   Add extracts or food coloring to customize your filling. Popular options include vanilla, raspberry, or chocolate.

3. Assemble the Macarons:

1. Match shells:
   Pair macaron shells of similar size.
2. Pipe the filling:
   Pipe a small amount of buttercream onto the flat side of one shell.
3. Sandwich the shells:
   Gently press another shell on top to create a sandwich. Repeat for all shells.
4. Rest and mature:
   Place the assembled macarons in an airtight container and refrigerate for 24 hours. This allows the flavors to meld and the shells to soften slightly.