Preheat oven to 350°F. Prepare muffin pan with paper baking cups.
In medium bowl, sift together flour, baking powder and salt; set aside. In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg and vanilla to butter mixture, mixing until well combined. Add flour mixture alternately with sour cream, beating well after each addition. Continue beating 1 minute. Pour batter into muffin cups until they are 2/3 full.
Bake 17-20 minutes or until toothpick inserted in center of cupcake comes out clean. Cool 5 minutes. Transfer to a cooling grid; cool completely before icing.