Line a baking sheet with parchment or a silicone mat and fit a piping bag with a round tip (4-6 mm or #10).

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

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

When soft peaks begin to form, gradually add the granulated sugar and continue to whisk until stiff, glossy peaks form and the sugar is dissolved.

Add the sifted almond flour and powdered sugar mixture to the whipped egg whites.

Fold gently with a spatula, adding food coloring if using. Continue folding until the batter flows off the spatula in a thick, continuous ribbon, described as 'lava'.

Do not overmix; you want the batter fluid enough to smooth but not so loose it collapses.

Transfer batter to the piping bag. On the prepared sheet, pipe heart shapes by drawing a small 'V' and then completing the rounded top.

Practice on a spare piece of parchment for consistent shapes.

Let the piped macarons sit at room temperature for 30 minutes to 1 hour or until a dry skin forms on the surface.

Preheat the oven to 300°F (150°C) and bake for 18-20 minutes.

The shells should be set, firm to the touch, and lift cleanly off the paper when done.

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

Gradually add the powdered sugar until combined, then stir in the vanilla and a pinch of salt.

Add the heavy cream one tablespoon at a time until the buttercream reaches a smooth, spreadable consistency.

Once shells are completely cool, flip them over and pipe a small amount of buttercream onto the flat side of one shell, sandwiching it with a matching-sized shell.

Refrigerate assembled macarons in an airtight container for at least 24 hours before serving for best texture and flavor.