Sift almond flour and powdered sugar together in a bowl. Discard any large bits.

In a stand mixer, beat egg whites to soft peaks. Meanwhile, heat granulated sugar and water in a saucepan to 240°F (115°C) to make syrup.

Slowly pour the hot syrup into the egg whites while beating on medium. Then increase to high speed and beat until the bowl is cool and you have stiff glossy peaks.

Fold the meringue into the almond flour/powdered sugar mixture in 3 additions. Gently fold until the batter flows like lava and forms a ribbon when lifted.

Transfer to a piping bag fitted with a round tip. Pipe small circles on a parchment-lined baking sheet. Tap the tray to release air bubbles.

Let them sit at room temperature for 30–45 minutes until the tops are dry to the touch.

Preheat oven to 300°F (150°C). Bake for 12–15 minutes. Let cool completely.

Beat egg yolk and sugar until light and fluffy. Slowly add softened butter and vanilla. Beat until creamy.

Pipe the buttercream onto half the macaron shells, then sandwich with the other half.

Chill for 24 hours for best texture. Bring to room temperature before serving.