In a small mixing bowl stir together flour, baking powder, soda, and salt; set aside. In a medium mixing bowl beat margarine or butter with an electric mixer on medium speed for 30 seconds. Add sugar; beat until fluffy. Add egg; beat well. Beat in apple butter and vanilla. Stir lemon juice into milk (mixture will curdle). Add flour mixture and milk mixture alternately to apple butter mixture, beating on low to medium speed after each addition just until combined.
Grease muffin cups or line with paper bake cups; fill two-thirds full. Bake in a 350 degrees F. oven for 20 to 25 minutes or until a toothpick inserted in the centers comes out clean. Cool on wire racks. If desired, frost with Penuche Frosting.
Penuche Frosting: In a small saucepan melt 1/2 cup margarine or butter; stir in 1 cup packed brown sugar. Cook and stir until bubbly. Remove from the heat. Add 1/4 cup milk; stir until smooth. Add 3-1/2 cups powdered sugar; beat by hand until of spreading consistency. Frost cooled cupcakes immediately. (If frosting thickens, stir in hot water, a few drops at a time, until of spreading consistency again.).