Preheat oven to 350 degrees. Beat butter and sugar at medium speed with an electric mixer until creamy. Add eggs, 1 at a time, beating until blended after each addition. Combine flour, baking powder, and salt; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Stir in vanilla.
Place paper baking cups in 2 (12-cup) muffin pans, and coat with cooking spray; spoon batter into cups, filling two-thirds full. Bake for 12-15 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely.
To prepare frosting, melt butter in a 3-qt. heavy saucepan over medium heat. Add brown sugar; bring to a boil, stirring constantly. Stir in evaporated milk, baking soda, and corn syrup; bring to a boil. Remove from heat, and let cool completely (about 1 hour). Transfer to a bowl. Gradually add powdered sugar to caramel mixture, beating at medium speed with an electric mixer until blended. Beat at high speed 2 minutes or until creamy. Use immediately. Make 3 cups.
Frost each cupcake with Old-Fashioned Caramel Frosting.