Butterscotch Muffins w/ Brown Sugar Topping

2 cups flour 1 cup sugar 1 (3 1/2 ounce) package instant butterscotch pudding mix 1 (3 1/2 ounce) package instant vanilla pudding 2 teaspoons baking powder 1[...]

1 cup unsalted butter , at room temperature 3 cups firmly packed golden brown sugar 4 large eggs 1 tablespoon vanilla extract 3 cups all-purpose flour 1[...]