Preheat oven to 375°F (190°C). Spray a 24-count mini muffin pan with nonstick spray or line with mini muffin liners. If using liners, I recommend lightly spraying them with nonstick spray. This recipe yields about 32 mini muffins, so prepare a second mini muffin pan in the same manner or bake in batches, keeping any leftover batter at room temperature while the first batch bakes.

In a medium bowl, whisk the flour, baking powder, baking soda, salt, and cinnamon together. Set aside.

In a large bowl, whisk the yogurt, melted butter or oil, and sugar together. Add the egg and vanilla, and whisk until combined. Finally, whisk in the milk.

Pour the dry ingredients into the wet ingredients and fold together just until combined. Do not over-mix. Gently fold in the mini chocolate chips. The batter will be slightly thick. Some small lumps are OK. Again, avoid over-mixing.

Spoon the batter into the prepared muffin cups, filling each about 3/4 full. Bake for 10–12 minutes, or until a toothpick inserted into the center of a muffin comes out clean. The muffins will still look fairly pale on top. Do not over-bake.

Allow the muffins to cool in the pan for 5 minutes, then transfer them to a cooling rack to continue cooling.

Cover leftover muffins tightly and store at room temperature for up to 5 days, or in the refrigerator for up to 1 week. If enjoying straight from the refrigerator, warm them in the microwave for a few seconds to soften them up, as they can taste a bit dense when cold.