1 (18.25 ounce) package spice cake mix
3/4 cup melted butter
4 eggs
1 (8 ounce) container sour cream
1 cup brown sugar
1 tablespoon ground cinnamon
2 cups confectioners' sugar
4 tablespoons milk
1 tablespoon vanilla extract

Preheat oven to 325 degrees F (165 degrees C).

In a large mixing bowl, combine cake mix, butter, eggs and sour cream. Stir by hand approximately 50 strokes, or until most large lumps are gone. Pour half of the batter into a 9 x 13-inch metal baking pan sprayed with cooking spray.

Combine the brown sugar and cinnamon, and sprinkle over the batter in the cake pan. Spoon the other half of the batter into the cake pan, covering the brown sugar and cinnamon. Swirl the cake with a butter knife or icing knife until it looks like a honey bun.

Bake for 40 minutes, or until a wooden pick inserted into the center of the cake comes out clean. Frost cake while it is still fairly hot. Serve warm.

Frosting: In a small bowl, whisk together the confectioner's sugar, milk and vanilla extract until smooth.