In a large bowl, add the dry ingredients and whisk to blend.
In a smaller bowl, add the wet ingredients and mix well.
Pour the wet ingredients into the dry ingredients and mix until blended.
In a small bowl, add the ingredients for the topping. Use a pastry blender to cut the cold butter into the ingredients so that it makes crumbles.
Pour the cake batter into a greased 8x8 baking pan.
Pour the crumble mixture on top and lightly press into the batter.
Bake for 40-45 minutes until done.
Allow to cool then slice.
I have tested this recipe with King Arthur Measure for Measure GF, Bob's Red Mill 1 to 1 GF blend, and Authentic Foods Multi Blend in this recipe. That doesn't mean others will not work, I just have not tested other flours.
If your gluten free flour blend doesn’t contain Xanthan Gum or Guar Gum, please add 1 teaspoon.
I highly suggest using almond flour and not almond meal. Almond meal is more coarse and will make your donuts grainy.
Other dairy-free kinds of milk will work but I do not recommend canned coconut milk.
To test for doneness, insert a toothpick into the center of the cake. If the toothpick comes out clean, it is done baking. If you see batter or crumbs, the cake needs to bake longer.
This cake will keep up to 3 days in an air-tight container, or up to 4 months in the freezer.