Rhubarb Big Crumb Coffee Cake This moist coffee cake features tart rhubarb and a generous cinnamon crumb topping. For the batter, mix 2 cups flour, 1 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp salt, 1/2 cup sugar, 1/2 cup sour cream, 1/2 cup butter, 2 eggs, and 1 tsp vanilla. Fold in 2 cups chopped rhubarb. For the crumb topping, combine 1 cup brown sugar, 1 cup flour, 1 tbsp cinnamon, and 1/2 cup melted butter. Pour batter into a greased pan, sprinkle crumbs on top, and bake at 175°C (350°