• Put oven rack in the middle position. Heat your oven to 350℉. Grease an 8 x 8 baking dish and set aside.

Make the topping

• In a microwave safe bowl, melt the butter for the crumb topping in 10 second bursts until fully melted. In a medium bowl, whisk together the flour, sugar, cinnamon, and salt for the crumb topping. Make a well in the flour mixture, and pour in the melted butter. Using a fork, mix together until there is no more dry flour. The mixture should be coarse and crumbly. Set aside.
  ⅓ + ¼ cup coconut sugar, 8 TBS melted butter, 1 tsp cinnamon, ¼ tsp kosher salt, 1 ¼ cup whole wheat flour

Make cake batter

• In a medium bowl, whisk the flour, sugar, baking powder, baking soda, cinnamon, and salt together. Set aside.
  ¼ cup coconut sugar, 1 ¼ cup whole wheat flour, 1 tsp baking powder, ¼ tsp baking soda, ½ tsp cinnamon, ¼ tsp kosher salt
• In a large bowl, mix together the milk and vinegar. Let sit for 5 minutes. Meanwhile, melt the butter for the cake the same way you melted the butter for the topping. Let butter cool.
  ½ cup milk, 1 TBS vinegar, 4 TBS melted butter
• After milk has thickened, add in the cooled melted butter, crack in the egg, and pour in the vanilla. Whisk together until homogenous.
  1 whole egg, 1 TBS vanilla extract
• Add the dry ingredients in the wet ingredients. Fold together until no more dry flour remains.
• Pour the batter into the prepared baking dish. Spread the batter into an even layer. Evenly sprinkle the topping onto the batter.
• Bake on the center rack for 25 minutes.
• Let cool for 10 minutes before cutting and enjoying.