Cake directions: Combine starter, water, and flour. Allow to ferment for 7 hours at room temperature or 72 hours in the fridge. When ready to bake, preheat oven to 350 degrees. Blend together egg white, buter, and extracts. Add blended ingredients to fermented batter. Mix well. Combine sweetener, salt, baking soda, and oat flour. Fold into batter along with grated apples. Set aside. Topping: Combine topping ingredients. Grease a 9 inch square baking pan. Pour 1/2 o f the batter into the baking pan. Sprinkle with 3/4 of the topping. Add remaining batter over the topping. Sprinkle with the last of the topping. Swirl knife through the batter. Bake for 30 minutes. Cool. Vanilla Syrup: Blend syrup ingredients together. Pour into a saucepan. Cook for 2 minutes. Serve over coffee cake. 9 servings.