Preheat oven to 350 degrees and spray an 8 x 13 baking pan with non-stick cooking spray
In a small mixing bowl, whisk together the flax egg ingredients. Let sit for at least 5-10 minutes, or until thickened.
In a large bowl, combine all the dry ingredients until combined.
Add the wet ingredients and the flax egg to the dry ingredients. Whisk the mixture together until combined and no streaks of flour remain.
In a small bowl, whisk together the streusel ingredients until combined.
Pour half of the wet batter into the prepared baking pan and spread out evenly. Sprinkle half of the brown sugar mix over the batter. Pour the rest of the batter over the cinnamon mixture and lightly spread it into the pan. Sprinkle the rest of the brown sugar evenly over the top.
Bake the cake for 36-40 minutes, or until a toothpick inserted into the cake comes out clean. Move the cake to a cooling rack and let it cool until at room temperature, or your desired serving temperature.
Notes
1. Leftover cake keeps covered at room temperature for up to 4-5 days. It can also keep in the freezer for up to 2-3 months. 2. To halve this recipe, use an 8 x 8 inch baking pan and bake the cake for 28-30 minutes. 3. Sprinkle 1 cup of any of the following mix-ins in with the cinnamon sugar to switch up this recipe: chocolate chips, raspberries, chocolate chips, dried cranberries, pecans, or walnuts.