Make the streusel:

1. In a small bowl, mix together all the streusel ingredients and set aside.

Make the crumble:

1. In a bowl, combine the flours, sugar, salt, and cinnamon. Add in the butter, working it in by flattening the pieces between your fingers and rolling your fingers, like you’re trying to snap them, to break them up into small, pea-sized pieces coated in the flour mixture. Set aside.

Make the cake:

1. Preheat the oven to 350F. Prep a 9×5 loaf pan by lining the long side with parchment paper (making a taco with the paper) and spray with nonstick spray.
2. In a large bowl, combine the flour, almond flour, baking soda, baking powder, and salt. Set aside.
3. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar. Beat for about 5 minutes, scraping the bowl occasionally to ensure a consistent texture. You are looking for a pale and fluffy mixture.
4. With the mixer on low, add the eggs one at a time, scraping down the bowl after each addition. Add the vanilla.
5. Alternating between adding 1/3 of the flour and 1/2 the sour cream until everything is incorporated. Mix until just combined.
6. Scoop half of the batter into the loaf pan. Sprinkle the streusel over the top. Scoop the remaining batter in and smooth it out with a wet finger or offset spatula.
7. Top with the crumble and bake for at least 50 minutes, (in my old oven it takes a full hour) or until a toothpick inserted into the center comes out clean.
8. Let the cake cool in the pan for 10 minutes. Run a knife around the sides of the pan to make it easier to release. Lift out the cake by the parchment paper and let it cool further on a wire rack for another 10 minutes.