4large eggs(use an egg substitute for a vegan option--See Recipe Notes / Special Diet Options for details)
Preheat oven to 315°F. Lightly oil a 9" x 9" baking dish; set aside.
For the Topping
In a small bowl, whisk together the butter (or coconut oil), honey, and cinnamon until well blended. Add the finely chopped walnuts (or other nut or seed) and toss well to combine. Set aside.
For the Cinnamon Swirl
In a small bowl, whisk together the butter (or coconut oil), honey, and cinnamon until well blended. Set aside.
For the Cake
In a food processor, combine the almond flour, coconut flour, baking soda, and salt. Add all of the remaining ingredients except the eggs and egg whites (or egg alternative) to the top of the dry ingredients in the order given. Cover and pulse a few times to combine. Then process until the batter is smooth and creamy (about 20-25 seconds).
Add the eggs and egg whites (or alternative). Cover and pulse a few times to combine. Then process just enough to blend the eggs into the batter (about 10-15 seconds). Use a thin spatula as needed to scrape down the sides.
Carefully spoon half of the batter into the prepared baking dish. Use an offset spatula to smooth out the top.
Drizzle with the cinnamon swirl across the top of the batter. Then carefully spoon the remaining cake batter on top. Use an offset spatula to smooth the top of the batter. Next, starting at the edges of the cake, crumble the topping evenly across the cake. Use your fingers to gently press the topping into the batter a bit.
Bake the cake for 45-55 minutes until light golden brown along edges and a toothpick inserted into center comes out clean. Allow the cake to cool on the stovetop about 5 minutes. Serve warm with your favorite coffee or tea.
While the recipe as written calls for honey, I have personally always used a low-carb sweetener and it's worked out fantastically. I use 1/2 - 3/4 of the amount since honey is sweetener than sugar. Personally I love using Lakanto or another erythritol / monk fruit sweetener. If using coconut oil, you will need to soften or melt in a pan in order to use it.