Sift almond flour and powdered sugar together into a bowl. Set aside.

In a clean, dry bowl, whip the egg whites with cream of tartar until foamy. Gradually add the granulated sugar while whipping until stiff, glossy peaks form. Add the pink food coloring and mix until evenly distributed.

Fold the almond flour and powdered sugar mixture into the meringue in two additions, until a smooth, lava-like batter forms (macaronage).

Fit a piping bag with a round tip and fill with the macaron batter. Pipe small heart shapes onto baking sheets lined with parchment paper.

Tap the baking sheets firmly on the counter to release air bubbles. Let the macarons rest at room temperature for 30-60 minutes, or until a skin forms.

Preheat oven to 300°F (150°C). Bake for 15 minutes, or until the shells are firm and have developed 'feet'. Let cool completely on the baking sheets.

In a bowl, beat the softened butter until creamy. Gradually add the powdered sugar, alternating with the heavy cream, beating until smooth and fluffy. Stir in the vanilla extract.

Pair up similar-sized macaron shells. Pipe or spread a small amount of buttercream onto one shell and sandwich with another.

Refrigerate the macarons for at least 30 minutes before serving to allow the flavors to meld.