Combine all of the ingredients for the walnut topping in a small bowl. Stir well to combine and set aside.

Preheat the oven to 350 degrees F and lightly butter or oil a 8" x 8" baking dish.

In a mixing bowl, stir together the coconut flour, arrowroot flour, baking powder, and salt.

In a separate bowl, whisk together the eggs, maple syrup, coconut milk, and butter. Pour this wet mixture into the bowl with the flour mixture and mix until smooth. Note: The batter will be thick.

Pour half of the cake batter into the prepared baking dish and spread evenly with a rubber spatula. Spread half of the walnut topping over the batter. Repeat for the remaining cake batter and walnut topping.

Bake on the center rack for 28 to 35 minutes or until cake tests clean when poked in the center (Note: mine took 32 minutes).

Allow cake to sit 20 minutes before cutting large chunks and serving.