1 egg yolk
1/2 teaspoon vanilla extract
1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon kosher salt
For the frosting:
2/3 cup granulated sugar
2 egg whites
1-1/2 cups (3 sticks) unsalted butter, at room temperature, cut into 2-inch chunks
1-2/3 cups confections' sugar
1/4 teaspoon kosher salt
2 tablespoons milk
1 tablespoon vanilla extract
About 2 tablespoons red or blue food coloring (optional) – experiment with the exact amount until you get your desired color, though I have a suspicion this frosting doesn't take coloring well. My red turned out more like hot pink.
For the decorations:
Thin red licorice cut into smaller pieces, blue and white candy, or decorations of your choice
For the cupcakes:
1. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well mixed. Set aside.
2. In large heatproof bowl, combine the chocolate and cocoa powder. In a small saucepan, heat the granulated sugar, butter, and water over medium-high heat, whisking occasionally, for 3 to 4 minutes, or until the butter is melted and the sugar is dissolved. Pour the hot butter-sugar mixture over the chocolate-cocoa mixture and whisk until the chocolate is completely melted and the mixture is smooth.
3. Whisk the milk, egg, egg yolk, and vanilla into the chocolate mixture until thoroughly combined.
4. Dump the flour mixture on top of the chocolate mixture. Whisk until the dry ingredients are totally mixed into the chocolate mixture.
5. Let the batter sit for at least 1 hour (I recommend longer) at room temperature, or transfer to an airtight container and store in the refrigerator for up to three days. (This allows the liquid to be totally absorbed into the batter, so the batter thickens up a bit and isn't so soupy.)
6. Preheat the oven to 350 degrees F. Butter and flour a muffin tin, or line with paper liners.