2 1/4 c. all-purpose flour
1 tsp. baking soda
1 tsp. baking powder
1 tsp. salt
1/2 c. (1 stick) unsalted butter, softened
1 1/2 c. sugar
1 tsp. vanilla
2 eggs
1 c. sour milk
1/3 c. hot tap water
1/2 c. unsweetened cocoa powder

COCOA BUTTER FROSTING:

1/2 c. (1 stick) butter, melted
1/2 c. unsweetened cocoa powder
2 tsp. vanilla
3 c. 10X (confectioners') sugar
3 tbsp. milk

1. Preheat oven to moderate (350 degrees).

2. Prepare cupcakes: Place cupcake liners in 24 medium size cupcake cups. Sift flour, baking soda, baking powder and salt onto waxed paper.

3. Beat together butter, sugar and vanilla in large bowl until light and fluffy. Add eggs; beat until well mixed. Mix in flour mixture alternately with sour milk, beginning and ending with flour.

4. Stir together hot water and cocoa powder in small bowl until smooth. Stir into batter. Beat 2 minutes at medium speed, scraping down side of bowl as needed. Divide batter into prepared cups using about 1/4 cup for each.

5. Bake in preheated moderate oven (350 degrees) for about 22-25 minutes or until a cake tester inserted in the center comes out clean. Remove cupcakes from the cups to wire racks, and let cool to room temperature.

6. Prepare the Cocoa Butter Frosting: Stir together the melted butter, cocoa and vanilla in a medium-size bowl. Add sugar and milk; stir until smooth, adding additional milk if necessary. Spoon the frosting into pastry bag that's fitted with a large star tip. Top each cupcake with a swirl of frosting.

Note: To make 1 cup sour milk, pour 2 tablespoons vinegar into 1 cup measure. Add milk to make 1 cup.