Cinnamon Swirl Coffee Cake Muffins

1. Preheat the oven to 350 F and line a 12-count standard size muffin tin with paper liners or spray with non-stick cooking spray.
2. For the streusel topping: In a medium bowl, combine all ingredients until the mixture resembles coarse crumbs. Set aside.
3. For the cinnamon filling: In a small bowl, combine all ingredients and mix well. Set aside.
4. For the muffins: Combine flour, sugar, baking powder, ground flax meal and salt in a large bowl. In a separate, small bowl, whisk together the oil, egg, and milk. Pour wet ingredient mixture over dry ingredient mixture and stir until well combined.
5. Fill each muffin cup 1/4 of the way with batter. Then add about 1 teaspoon of cinnamon filling over the first layer of batter. I used a butter knife for an easier way to spread the cinnamon filling over the muffin batter. Add another layer of batter over the cinnamon filling, until the muffin cups are 3/4 full.
6. Cover muffins with streusel topping, then bake at 350 F for 15-20 minutes or until a toothpick comes out clean.
7. Let the muffins cool in the pans for about 5 minutes before transferring to a wire rack to cool completely.

Adapted from On Sugar Mountain.