Preheat oven to 350 degrees. Line a muffin tin with muffin liners and set aside.Prepare the crumb topping. In a small bowl, combine ¼ cup flour with the melted butter and brown sugar. Set aside. *Note – this mixture will be smooth at first. Once it has cooled, you can poke and fluff it with a fork to make it crumbly.Prepare the wet ingredients. In a large bowl, beat the oil, applesauce, and sugar until well combined (about 1 minute). Beat in the eggs. Then, add the milk, lemon zest, lemon juice, and vanilla. Beat to combine.Prepare the dry ingredients. In a medium bowl, add 1½ cups of flour, the baking powder, baking soda, and salt. Stir to combine. Add the frozen blueberries. Stir gently to coat the blueberries in flour.Add the dry ingredients to the wet ingredients. Stir just until the flour is moistened. Do not over mix (batter should be lumpy).Fill the muffin cups ¾ of the way up with batter. Crumble the topping by poking with a fork. Sprinkle the crumb topping on the muffins. Bake for 22-24 minutes, or until a toothpick inserted into the center comes out clean. Cool completely in muffin tin.