Combine the sugar, butter, almond milk, flax, and vanilla and set aside.
Into another bowl, sift together the flours, baking powder, cinnamon, and salt.
Gradually combine the wet and dry ingredients and gently stir together. Fill a greased 8×8 or 7×9 baking pan (or 12 muffin cups) with the batter.
Make the crumbly topping: In a small bowl, use a fork or your hands to combine the butter, sugar, flour, cinnamon, and nuts, if using. Mix until just crumbly. Add more flour if the mixture is too wet.
Sprinkle ½ of the crumble mixture over the cake and bake for 25-30 minutes.
Sprinkle the last half of the crumble mixture over the cake after it comes out of the oven.
Recipe by Love and Lemons at https://www.loveandlemons.com/?p=1835