Bake the macaron shells according to the recipe directions.

Place the champagne in a small pot, and cook over medium-low heat until reduced by more than half. (You should have about 3 tablespoons.) Set aside and allow to cool completely.

Arrange 5 or 6 fresh raspberries around the outside edges of half the macaron shells.

Place the egg whites and sugar in a large metal mixing bowl and set over a pot of barely simmering water. Cook, whisking occasionally, until the mixture is very warm to the touch and no longer feels gritty when rubbed between the thumb and forefinger (about 5 minutes). Remove the bowl from the heat and whip on medium-high speed until stiff and glossy and completely cool. (There should be no hint of warmth when you place your hand on the side of the bowl.) Whip in the butter, a tablespoon at a time. (If the buttercream seems runny, place the entire bowl + whisk in the refrigerator for 10 to 20 minutes, then re-whip.) Stir in the reserved champagne reduction and transfer the mixture to a pastry bag fitted with a 2A tip.

Pipe a small amount of buttercream into the well created by the raspberries. Sandwich with remaining macaron shells.