Mixing: Preheat oven to 375 degrees F. In a bowl combine flour, Gentle Sweet, baking powder, baking soda and salt, Set aside. In a separate bowl blend together sourdough starter, eggs, egg whites, vanilla, and yogurt. Add chopped rhubarb and strawberries to the dry ingredients. Stir to coat. Add the dry ingredients to the wet ingredients. Stir until just combined.