Cream butter, gradually add sugars, beating well at medium speed of an electric mixer. Add eggs, one at a time, beating after each addition.
Combine flour, baking powder, soda, salt, and cinnamon; stir well. Add flour mixture to the creamed mixture alternately with the buttermilk, beginning and ending with the flour mixture.
Pour batter into a greased and floured 13x9x2 inch baking pan. Sprinkle topping evenly over cake. Cover and chill 8 hours. Bake at 350 degrees for 40 to 45 minutes or until lightly browned. Cut coffee cake into squares.
Combine brown sugar, pecans, nutmeg, and cinnamon in a small bowl, stirring well.