In a large bowl, combine the cake ingredients in a large mixing bowl and whisk to blend.
In a smaller bowl, add the wet ingredients and whisk to mix.
Pour the wet ingredients into the dry ingredients and mix until just "barely" mixed. This will help keep your cake light and fluffy.
Spray a 9" cake pan or loaf pan with non-stick spray and add half the cake batter. Spread it out.
For the Swirl:
Mix up the cinnamon and sugar for the swirl and sprinkle it around the cake batter. Put the rest of the cake batter on top and spread it out.
For the Streusel:
Preheat the oven to 350º F
In a bowl, add the crumble topping dry ingredients.
Add the softened butter and mix. Freeze the crumble topping for 15-20 minutes then use a fork to crumble the slightly hardened mixture.
Sprinkle the crumble topping over the cake batter.
Spread out the crumble topping and bake at 350º F for 30-35 minutes. Actual baking time can vary greatly depending on if you bake this in a loaf pan or cake pan, and how deep your pan is.
To tell if the cake is done baking, take out the cake and insert a toothpick into the middle of the cake. If the toothpick comes back with crumbs or batter, it will need to bake more. If the toothpick comes out clean, the cake is finished baking.
I have tested this recipe with King Arthur Measure for Measure GF and Bob's Red Mill 1 to 1 GF blend. 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.
To make this recipe dairy-free, substitute the butter for vegan butter.
I used almond milk but other dairy-free kinds of milk will work but I do not recommend canned coconut milk.
To keep your cake light and fluffy, do not overmix your cake batter.
Freezing the streusel topping will make it hold its shape better while baking.
This cake will keep up to 4 days in an air-tight container, or up to 4 months in the freezer.