Preheat oven to 375 degrees F. Line an 8×8 square baking pan with parchment paper and set aside.
In a glass liquid measuring cup, make the vegan buttermilk by combining the almond milk and vinegar. Set aside.
In a medium bowl, make the flax egg by combining the ground flaxseed and water. Stir and set aside for 5 minutes to thicken.
Then, make the crumble. In another medium bowl, add the flour, sugar, and cinnamon. Stir until combined. Add the melted coconut oil and stir until combined. Place in the fridge while you make the cake. It will firm up a little in the fridge.
In a large bowl, add the flour, baking powder, baking soda, and salt. Whisk until well combined.
In the medium bowl with the flax egg, add the melted butter, sugar, yogurt, vegan buttermilk that you made, and vanilla. Whisk until well combined.
Add the wet to the dry. Stir with a spatula until just combined. Don’t overmix it. Fold in the blueberries (make sure you toss the blueberries in 2 Tbsp of flour before adding it to the batter). Careful not to overmix again.
Pour batter into the lined pan. Take the crumble out of the fridge and break it up a bit. Sprinkle evenly all over the top of the batter. Bake in the oven for 40-45 minutes or until a toothpick comes out clean and the top is lightly golden. Let it cool in the pan for 15 minutes, then carefully transfer the cake out of the pan and let it cool on a wire rack. Slice and enjoy! Store leftovers in an airtight container on the counter for up to 3 days.