Preheat oven to 350°. Line 24 muffin cups with paper liners.

In a medium saucepan, cook butter, chocolate, and cocoa powder over medium-low heat, stirring frequently, until melted and smooth. Let cool for 15 minutes.

In a large bowl, beat sugar and eggs with a mixer at high speed until thick and pale. In a medium bowl, whisk together flour and next 3 ingredients. Gradually add flour mixture to egg mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition; stir in chocolate mixture. Spoon batter into prepared muffin cups.

Bake for 14 to 16 minutes or until a wooden pick inserted in center comes out clean. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks. Pipe or spread Cherry Buttercream onto cupcakes. Cover and refrigerate for up to 3 days.

In the top of a double boiler, whisk together sugar and egg whites until combined. Cook, without stirring, over simmering water until a candy thermometer registers 140°. Immediately pour mixture into the work bowl of a heavy-duty stand mixer and beat at high speed for 10 minutes.

Reduce speed to medium-low, and add butter, 2 tablespoons at a time, beating just until combined after each addition. Beat in syrup until combined. Store buttercream at room temperature until ready to use.