Make Crumb Topping:
Prepare crumb topping: In a large bowl, combine granulated sugar, brown sugar, cinnamon, salt, and flour. Pour in melted butter and mix until the mixture forms coarse crumbs. Lightly toss with a fork and reserve.Mix Dry Ingredients:
Prepare muffin batter: In a separate large bowl, whisk together flour, brown sugar, baking powder, baking soda, cinnamon, and salt.Combine Wet Ingredients:
In a medium bowl, beat eggs, then whisk in milk, oil, and vanilla extract.Mix Batter Until Just Combined:
Pour wet mixture into dry ingredients and stir with a wooden spoon until just incorporated; batter should be lumpy. Avoid overmixing.Fill Muffin Cups:
Divide batter among muffin cups, filling each about three-quarters full.Add Crumb Topping:
Evenly distribute reserved crumb topping over each muffin, using all of it even if it appears excessive.Bake Muffins:
Bake for 15–18 minutes, or until a toothpick inserted in the center of a muffin emerges clean (may need up to 20 minutes; ovens differ).Cool Muffins:
Cool muffins in the pan for 10 minutes, then transfer to a wire rack to cool completely.