Line 2 baking sheets with parchment paper and set aside.

Place 1 cup powdered sugar and 1/2 cup almond flour in a bowl and sift together, discarding any coarse bits. Set the mixture aside.

In a clean, dry mixing bowl, add the room-temperature egg whites. Beat on low speed until foamy.

Gradually add the granulated sugar while mixing, then increase to medium-high speed and beat until stiff, glossy peaks form.

Add 1/2 teaspoon vanilla bean paste and, if desired, a few drops of red or pink food coloring to the meringue and mix just until blended.

Add the almond flour and powdered sugar mixture to the meringue. Gently fold with a spatula, scraping around the bowl and pressing some batter against the sides, until the batter flows in a thick ribbon and slowly melts back into itself.

Transfer the macaron batter to a piping bag fitted with a round tip.

On the prepared baking sheets, pipe small heart shapes by drawing a “V” and rounding the top, keeping the hearts similar in size.

Tap the baking sheets firmly on the counter several times to release any air bubbles.

Let the piped hearts rest at room temperature for 30 minutes, or until the tops feel dry to the touch and a skin has formed.

While the shells rest, preheat the oven to 300°F.

Bake one tray at a time for 18 to 20 minutes, until the shells are set, have developed feet, and lift easily from the parchment when gently nudged.

Remove from the oven and let the shells cool completely on the baking sheets.

To make the buttercream, beat the softened butter in a bowl until smooth and creamy.

Add 1 cup powdered sugar, 1 teaspoon vanilla bean paste, and a pinch of salt, beating until fluffy.

Add the heavy cream or milk, 1 tablespoon at a time, mixing until the buttercream is smooth and spreadable. Add red food coloring if you want a pink filling and mix to combine.

Carefully remove the cooled macaron shells from the parchment and pair them by similar size and shape.

Transfer the buttercream to a clean piping bag fitted with a small round tip.

Pipe a small dollop of buttercream onto the flat side of one shell in each pair, then gently press a matching shell on top to form a sandwich.

Place the assembled macarons in an airtight container and refrigerate for at least 24 hours before serving to allow the texture and flavor to mature.