Preheat the oven to 375° F. Line muffin tin with paper cups or spray with a baking spray.
Make the topping
In a large mixing bowl, whisk together granulated sugar, brown sugar, cinnamon, salt, and flour. Add melted butter and stir in until it all comes together. Fluff with a fork to make a mixture that resembles coarse crumbs.
Make muffins
In another mixing bowl, whisk together flour, brown sugar, baking powder, baking soda, cinnamon, and salt. Whisk together eggs, milk, oil and vanilla extract in a different bowl. Add the wet ingredients to the dry ingredients and stir it all together with a wooden spoon, just until combined. Don't' over-mix. The batter should be lumpy.
Using a spring release scoop, scoop the batter into the muffin tin filling it about 3/4 full. Sprinkle the topping on top of the batter of each muffin. It will seem like a lot of streusel but pile it on and use it all.
Bake the muffins for 15 to 18 minutes or until the toothpick inserted into a muffin comes out clean. It may take even 20 minutes (each oven is different, therefore, check the doneness with a wooden pick the first time you make them)
Let the muffins cool in the pan for 5 minutes, then transfer onto a cooling rack to cool completely.