To prepare cupcakes: Line twelve 2- ½-inch muffin cups with paper bake cups. Coat paper bake cups with cooking spray. (Or grease and lightly flour the muffin cups.) Set aside. In a medium bowl, combine flour, baking powder, baking soda, and salt; set aside.
In a small bowl, whisk together buttermilk, sugar, oil, egg product, and vanilla extract. Add buttermilk mixture to flour mixture. Beat with a wire whisk just until combined.
Spoon batter evenly into prepared muffin cups, filling each two-thirds to three-fourths full. Bake for 14 to 16 minutes or until a toothpick inserted near centers comes out clean. Cool in muffin cups on a wire rack for 5 minutes. Remove cupcakes from muffin cups. Cool completely on wire rack.
To prepare frosting: Beat cream cheese in a bowl with a mixer on medium until smooth. Beat in yogurt and 2 tablespoons cocoa powder until smooth. Beat in powdered sugar until smooth (frosting will thin slightly). Cover and chill 4 to 24 hours before spreading or piping on cupcakes.
Using a pastry bag fitted with an open star tip, pipe frosting onto cooled cupcakes. If desired, dust with 1 teaspoon cocoa powder. Store frosted cupcakes in refrigerator.
Tips: You may substitute ½ cup whole-wheat pastry flour for ½ cup of the all-purpose flour if desired.
To make ¾ cup sour fat-free milk, place 2 teaspoons lemon juice or vinegar in a glass measuring cup. Add enough fat-free milk to measure ¾ cup total liquid; stir. Let stand for 5 minutes before using.
If using a sugar substitute in place of granulated sugar, choose Splenda® Sugar Blend for Baking or Sun Crystals® Granulated Blend. Follow package directions to use product amount equivalent to sugar amount called for. Nutrition per frosted cupcake with sugar substitute: same as below, except 192 cal., 23 g carb. Exchanges: ½ other carb. Carb Choices: 1½.