First, combine the plant milk with the apple cider vinegar and let it sit for 10 minutes to create a vegan buttermilk. Line an 8×8 square baking pan with parchment paper and set aside. Preheat the oven to 350 degrees F. While the vegan buttermilk is curdling, combine the almond flour, cassava flour, coconut flour, cinnamon, salt, baking powder, and baking soda in a large bowl and whisk to combine. Set aside.

Now make the cinnamon layer. Simply whisk together the coconut sugar, cinnamon and pinch of salt in a separate bowl.

Make the streusel topping by combining all of the streusel ingredients in a bowl to create a crumb-like texture. You can use a fork or your hands to do this.

Next, add the pure vanilla extract, maple syrup, avocado oil, and apple juice to the large bowl with the flour mixture. Add the vegan buttermilk and fold the batter together just until there is no dry flour left. The consistency should be very cookie dough-like, not runny. Press half of the batter into the baking sheet, top with the cinnamon layer, add the remaining half of cake batter on top of the cinnamon layer evenly, and then spread the streusel topping over top. Bake for 45-50 minutes and let the coffee cake cool completely before slicing. Drizzle the icing over top if desired and enjoy!

NOTE: It's best to store the coffee cake on your counter UNCOVERED for the first day. If you cover it, it becomes too soft. This cake is actually better the second day after it has “dried out” just a little bit, then you can loosely cover it and enjoy within 3-4 days.