Sift the powdered sugar and almond flour together into a bowl to ensure a fine, lump-free mixture. Set it aside.

In a separate clean mixing bowl, whisk the egg whites with a hand or stand mixer, starting on low speed and increasing to medium-high.

When soft peaks form, gradually add the granulated sugar, whisking until stiff peaks form.

Gently fold in the sifted almond flour and powdered sugar mixture with a spatula. Add food coloring if desired, folding until it flows off the spatula like thick lava.

Transfer the macaron batter into a piping bag with a round tip. On a lined baking sheet, pipe heart shapes by drawing a 'V' shape and completing the heart.

Allow the piped macarons to sit at room temperature for 30 minutes to 1 hour to form a dry skin.

Preheat the oven to 300°F (150°C). Bake the macarons for 18 to 20 minutes until they are firm to touch and lift off easily.

In a medium bowl, beat the softened butter until smooth and creamy.

Add the powdered sugar gradually, one tablespoon at a time, mixing well.

Mix in the vanilla extract and a pinch of salt.

Add heavy cream or milk until reaching a smooth, spreadable consistency. Add food coloring if desired.

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

For best flavor and texture, chill the assembled macarons in the refrigerator for at least 24 hours before serving.