Preheat oven to 350 degrees and grease an 8x8 pyrex or cake pan.
Combine oat flour, buckwheat flour, protein powder, coconut sugar, baking powder, salt and cinnamon in a large bowl.
Whisk together egg, applesauce, yogurt, almond milk and vanilla extract in a small bowl.
Pour wet ingredients into dry and mix until fully incorporated.
Pour batter into the prepared baking dish.
Combine sugar + cinnamon and sprinkle over the batter, swirl into the entire surface of the batter using a knife or toothpick.
Bake for about 25-30 minutes or until toothpick inserted in the center of the cake comes out clean.
Let cool in pan for 10-15 minutes before slicing.
Store in the refrigerator in an airtight container.
Video
Notes
-Oat and buckwheat flour can be ground in a food processor or blender from rolled oats and buckwheat groats, respectively.-Original recipe called for turbinado (raw) sugar, I used coconut sugar in this updated version. Either will work.-Adapted from Jamie Eason's Cinnamon Swirl Bread