Prepare a 9-inch round or square cake pan by buttering it generously. You can also place a piece of parchment paper across the bottom with extra paper running up the sides. This creates little tabs to help pull the cake out of the pan if needed.
Preheat oven 350 degrees. In a large mixing bowl, place all the dry ingredients and whisk together to combine completely. Cut in the butter with knives or your hands until the butter is the size of peas.
Measure the milk and apple cider vinegar together and let sit for a few minutes before stirring in the egg. Gently stir the wet ingredients into the dry ingredients, mixing only until they are incorporated and no dry flour remains visible.
Spoon into the prepared pan and spread evenly with the back of the spoon or spatula. Prepare the crumb topping by combining all ingredients in a bowl.
Sprinkle the blueberries on top on the cake and press into the dough with a spoon or spatula. Cover the blueberries with the crumb topping and place into the warm oven. Bake until golden brown and the cake springs back when it is touched gently, approximately 45 minutes.