Instructions

1. Preheat oven to 425°F. Line a muffin tin with 10 muffin cups, and spray the muffin cups with an oil-based spray. Set aside.
2. First, make the cinnamon sugar swirl mixture in a microwave safe bowl, microwave the butter, sugar, cinnamon, and salt in 20 second increment, stirring between each. Repeat until the mixture is homogenous and the butter is fully melted. Transfer the mixture to a piping bag and set aside.
3. In a large bowl, combine the  brown sugar, eggs, melted butter, greek yogurt, and vanilla extract.
4. In a separate bowl, mix together the flour, cinnamon, baking powder, salt, and chocolate chips.
5. Fold the dry ingredients into the wet, mixing only until combined. Having a few lumps in the batter is totally fine!
6. Scoop batter into prepared muffin cups, filling just shy of the top of the cups. Snip off the top of the piping bag for the cinnamon sugar mixture and stick the bag into each muffin at varying depths, injecting each muffin a few times. Bake for 5 minutes at 425°F, then, without opening your oven door, turn the oven down to 350°F and bake for an additional 15 minutes.
7. Remove from oven and allow to cool for 10 minutes, before transferring to a wire rack to cool completely.