Preheat the oven to 375 degrees and line a 9’’ baking pan with parchment paper.
In a small bowl, mix together the almond milk and apple cider vinegar. Let sit for 10 minutes (this becomes vegan buttermilk).
In a medium mixing bowl, mix together all of the pecan crumble ingredients and set aside.
Grate apples and squeeze out any excess water with a cheesecloth or dish towel.
In another medium bowl, mix together all the dry base ingredients (oat flour, coconut sugar, baking powder, salt). Add in wet ingredients (buttermilk, vegan butter, vanilla, and apples) and mix together well.
Place the base batter into the baking pan and use a spatula to make sure it is even.
Sprinkle the crumble over the entire top of the base so that it is fully covered.
Cook for 20 minutes and let cool, then ENJOY!