Gluten-free Soy-free Recipe. Stir in the sweet potato, soy milk, vanilla, and sugar. Bake for 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Cook Time 45 mins. Evenly divide cake batter between prepared cake pans. Add sweet potato purée, water, oil, vinegar, and vanilla and whisk well to form a smooth batter. In a large mug, whisk together the egg substitute and water with a fork and set aside for 5 minutes to thicken. Prep Time 5 mins. Makes 8 by 8 inch brownie pan. Vegan Gluten free Coffee Cake - Sweet Potato Pecan Crumb Cake. Allow cakes to cool for 15 minutes in pans. Warm Cozy slice of cake. Vegan Gluten free Coffee Cake - Simple Fall Sweet Potato Pecan Crumb Cake with Pumpkin pie spices. Total Time 50 mins.