Preheat oven to 350°.
To prepare cupcakes, place 1/4 cup butter and granulated sugar in a large bowl; beat with a mixer at medium speed until blended. Add egg substitute; beat well. Add banana and 1 teaspoon vanilla; beat 1 minute.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, and 1/4 teaspoon salt in a bowl; stir with a whisk. Add flour mixture and milk alternately to sugar mixture, beginning and ending with flour mixture.
Line 12 muffin cups with paper liners; fill cups with batter. Bake at 350° for 20 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes on wire rack; remove from muffin tin, and cool completely on a wire rack.
To prepare frosting, combine cream cheese, peanut butter, and 3 tablespoons butter in a medium bowl; beat until light and fluffy. Add powdered sugar, 1/2 teaspoon vanilla, and dash of salt. Spread frosting evenly over cupcakes; sprinkle evenly with peanuts.