Black-and-White Cupcakes

Preparation

1. To Make the Cupcakes

   1. Step 1

      Position the racks to divide the oven into thirds, and heat to 350 degrees. Line 18 muffin cups with cupcake papers, or grease the tins.

   2. Step 2

      Whisk together the flour, baking powder, baking soda and salt.

   3. Step 3

      Working with a mixer, beat the butter and sugar together on medium speed until light and fluffy, 3-4 minutes. Add the whole eggs and the yolk one at a time, mixing well after each goes in. Beat in the vanilla.

   4. Step 4

      On low speed, mix in the dry ingredients in three additions and the buttermilk in two, scraping the bowl, as needed, and beating until the batter is smooth. Mix in the chips.

   5. Step 5

      Divide the batter among the muffin cups. Bake for 20-22 minutes — rotating the pans top to bottom and front to back after 10 minutes — or until the tops feel springy to the touch (they won’t color much) and a toothpick inserted into the center comes out clean. Cool in the pans for 10 minutes, then transfer to a rack to cool to room temperature. Frost, and cover with sprinkles, if you’d like, before the frosting dries.

2. To Make the Frosting

   1. Step 6

      Put the chocolate in a heatproof bowl, and fit it into a saucepan of simmering water — don’t let the bottom of the bowl touch the water. Melt the chocolate, stirring occasionally. Remove the bowl from the heat, whisk in the sugar and let rest on the counter for 3 minutes. Bit by bit, whisk in the cold butter, mixing until smooth and thickened just enough to spread. Use immediately.