Chocolate cupcakes

1/4 pound unsalted butter, at room temperature 1 cup sugar 4 extra-large eggs, at room temperature 8 fluid ounces chocolate syrup (recommended: Hershey's) 1 Tablespoon pure vanilla extract 1 cup all-purpose flour 1 Tablespoon coco 1/2 cup sour cream Line muffin pans with 24 paper liners. Preheat the oven to 325 degrees F. Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment until light and fluffy. Add the eggs, 1 at a time. Mix in the chocolate syrup and vanilla. Add the flour (with coco mixed in) and mix until just combined. Don't overbeat, or the cupcakes will be tough. Scoop the batter into the muffin cups and bake for 30 minutes, or until just set in the middle. Don't overbake! Let the cupcakes cool thoroughly in the pan.