Sift the powdered sugar and almond flour together into a bowl, ensuring a fine mixture.

In a clean mixing bowl, whisk the egg whites with a hand or stand mixer on low speed, increasing to medium-high until soft peaks form. Gradually add the granulated sugar and continue whisking until stiff peaks form.

Gently fold the sifted mixture into the whipped egg whites without deflating them. If desired, add food coloring and continue folding until the batter flows like thick lava.

Transfer the batter into a piping bag fitted with a round tip. Pipe heart shapes on a baking sheet lined with parchment paper.

Allow the piped macarons to rest at room temperature for 30 minutes to 1 hour until a dry skin forms.

Preheat your oven to 300°F (150°C).

Bake the macarons for 18 to 20 minutes until firm and easily lift from the parchment paper.

Beat the softened butter in a medium mixing bowl until smooth and creamy.

Gradually add powdered sugar, one tablespoon at a time, beating thoroughly. Stir in vanilla extract and a pinch of salt.

Add heavy cream or milk gradually until a smooth and spreadable consistency is achieved. Optionally, add red food coloring if desired.

Once the macaron shells have cooled, flip them over. Pipe a small amount of buttercream on the flat side of one shell and sandwich it with another.

For best flavor and texture, refrigerate assembled macarons for at least 24 hours.