To add a streusel topping to your dairy-free apple cinnamon muffins, combine 1/4 cup of granulated sugar, 1/4 cup of all-purpose flour (or gluten-free flour blend), and 1/2 teaspoon of ground cinnamon in a small bowl. Cut in 2 tablespoons of dairy-free butter or coconut oil until the mixture resembles coarse crumbs. Sprinkle the streusel evenly over the muffin batter before baking, and then proceed with the baking instructions as usual.