Combine flour, brown sugar, salt, and cinnamon together in a small mixing bowl. Mix in the butter until just crumbly, using 2 forks or your fingers. Set aside to top muffins.
For the Gluten-Free Muffins
Preheat oven to 375 degrees F and line muffin tin with muffin liners or grease really well.
In a large bowl, gently whisk flour, brown sugar, baking powder, baking soda, cinnamon, and salt together.
In a smaller bowl, whisk milk, oil, eggs and vanilla until completely combined. Make a well in the center of dry mixture and pour in liquid. Mix until just combined, being cautious to not overmix the batter.
Scoop ¼ cup of the batter into the prepared muffin tin. Sprinkle the crumble evenly over the muffin, gently pressing the crumble into each muffin.
Bake the muffins for 15-17 minutes or until a toothpick inserted into the center come out dry.
Cool on a rack for 10 minutes and then remove muffins from pan. Allow to cool fully before storing.
Video
Notes
To keep these muffins Egg-Free, use ⅓ cup water mixed with 2 tablespoons of ground flaxseed in place of the two eggs. For dairy-free muffins, use almond milk in place of the milk and solid coconut oil in place of the butter in the crumb topping. Crumb Topping: Feel free to skip the crumb topping.Flour Options: If you are NOT gluten-free, go ahead and make these Cinnamon Streusel Muffins with whole wheat or unbleached flour (it is an equal substitution).Storage: Store muffins in an air-tight container for 3 days at room temperature and up to 5 days in the refrigerator. The muffins can be frozen for up to 3 months.