Preheat oven to 350F. Lightly grease a 10 x 10 inch ( or larger if needed) baking dish. Take out two bowls. In the first bowl, mix together the coconut milk and apple cider vinegar (this essentially creates the buttermilk). Whisk for about a minute, then let it sit.
In the other mixing bowl, using a whisk, stir the flour, baking powder, salt and sugar until nicely combined.
Add in the canola oil and applesauce into the coconut milk mixture. Whisk until nicely combined. Then, pour in the dry ingredients into the bowl with the coconut milk mixture. Using a hand mixer, mix the ingredients until nicely combined. Add in the blueberries and gently mix using your handheld mixer (I don't mind breaking apart some of the blueberries with the mixer as it adds in some great flavor!)
Pour in the mixture into the baking dish.
For the topper, in a separate bowl, using your hand mixer, cream the vegan butter. Add in the brown sugar, and mix for 1 minute until somewhat crumbly. Scoop it our and - as best as you can - generously sprinkle it equally on your cake.
Put it in the oven for about 55 minutes (my oven sometimes take a bit longer, so anywhere between 45 - 65 minutes should work!) Let it cool then enjoy. It's also delicious served warm or with a scoop of ice cream.