Prepare any optional topping in advance (see post). Prep a 9 X 13 or similar pan well for nonstick. Preheat your oven to 325.
In a bowl, mix together your flour and baking soda. Set this bowl aside. Next, in a smaller bowl, blend together ½ cup of the sugar alternative and cinnamon. You can add any optional nuts here as well. Set this bowl aside as well.
In a mixing bowl, combine together the butter and 2 cups of sugar alternative. When smooth you can add the eggs, one at a time and then the vanilla, mixing between additions.
Now in this step we will alternate adding the sour cream and the flour mixture to the mixing bowl. Add ½ of each at a time, mixing between additions.
For this step we will be using layers to create the cake. Pour half of the batter from the mixing bowl into the prepped pan. Cover this with the sugar alternative and cinnamon mix from the smaller bowl. Then cover with the remaining batter. For more layers simply pour in thirds instead of halves
If adding the crumble topping do so now. However, you may want to loosely cover this or tent over it half way through baking if this browns too fast.Bake your coffee cake for 45-50 minutes or until a toothpick comes out clean. Allow your cake to cool before covering with a glaze