Preheat oven to 375℉ (190℃) and line muffin tin with muffin liners or grease really well.
Prepare the streusel in a small mixing bowl by combining ½ cup 1:1 gluten-free all-purpose flour blend, ¼ cup brown sugar, 1 teaspoon cinnamon, and ¼ teaspoon kosher salt. Mix in softened 3 tablespoons unsalted butter until just crumbly, using 2 forks or your fingers. Set aside to top muffins.
In a large bowl, whisk together 1 ½ cups 1:1 gluten-free all-purpose flour blend, ½ cup brown sugar, 2 teaspoons baking powder, ¼ teaspoon baking soda, 1 teaspoon ground cinnamon, and ⅛ teaspoon kosher salt until well combined.
In a smaller bowl, whisk ¾ cup milk, ⅓ cup canola oil, 2 large eggs, and 2 teaspoons vanilla extract until completely combined.
Make a well in the center of dry mixture and pour in liquid. Using a gentle hand, fold the batter together until the dry ingredients are just moistened, 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.
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Notes
Egg-Free: Combine 6 tablespoons of water with 2 tablespoons of ground flaxseed and let sit for 5 minutes. Use to replace 2 large eggs. Dairy-Free: Use non-dairy milk in place of the milk and your favorite non-dairy butter in the streusein 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 or up to 5 days in the refrigerator. The muffins can be frozen for up to 3 months.