Coat a 9"x5" loaf pan with butter; set aside. In a small bowl, stir together 1/3 cup sugar and 3 teaspoons cinnamon; set aside. In a large bowl, sift together flour, baking powder, salt and remaining cinnamon and remaining sugar. In another bowl, whisk together egg, milk, oil and vanilla. Add egg mixture to flour mixture; stir just until combined. Pour half of batter into loaf pan; sprinkle with half of cinnamon-sugar. Add remaining batter; use a knife to swirl batter. Top with remaining cinnamon-sugar. Bake at 350 degrees for 45 minutes, or until a toothpick inserted in the center comes out clean. Cool in pan on a wire rack for 10 minutes. Remove loaf from pan onto a plate or small platter. Carefully press all the sides of the loaf into any cinnamon-sugar that comes off onto the plate. Slice and serve. Makes one loaf.