Preheat the oven to 400 degrees F. (204 C) Mix the salt, baking, powder, and flour together. I just use a whisk to do this. A sifter works well too.
In a large bowl, whisk together the egg and the milk, then add in the oil, vanilla extract, and the sugar and mix it all together. You can use an electric mixer as well.
Add the flour mixture a third of it at a time to the wet ingredient mixture until completely mixed in. If you are using a whisk, you will need to switch to a wooden spoon or something, most likely.
Gently fold in the blueberries with a spatula. If you are using frozen blueberries don't thaw them out, just use them frozen.
Line a muffin pan with 9 to 12 muffin cups. If you want them larger, use 9, or regular size, use 12. Use a spoon and fill the cups 2/3 to 3/4 full. If you don't have muffin cups, you can spray the pan with cooking spray.
Time to make the crumble topping. Mix together the flour, cinnamon, sugar, and softened butter. First, start with a fork or pastry blender and mix it together. Then you can use your clean fingers which works really well!
Sprinkle the crumble evenly across all the muffins. Then bake on the middle rack for 20 to 25 minutes until a toothpick comes out clean. Allow them to cool for a few minutes before serving. Enjoy!