Preheat oven:
Preheat to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease it with cooking spray.

Mash bananas:
In a large bowl, mash ripe bananas with a fork until mostly smooth with small chunks remaining.

Combine wet ingredients:
Add melted (slightly cooled) butter, sugar, eggs, and vanilla extract. Whisk until smooth and creamy.

Whisk dry ingredients:
In another bowl, whisk together flour, baking soda, salt, and cinnamon until evenly combined.

Mix wet and dry:
Add dry ingredients to wet ingredients and stir until just combined. Avoid overmixing to keep muffins tender.

Add milk:
Gently fold in the milk until incorporated. The batter should be thick but scoopable.

Add optional mix-ins:
Fold in chocolate chips, nuts, or blueberries if desired.

Fill muffin cups:
Divide batter evenly among muffin cups, filling each about ¾ full.

Bake:
Bake for 18–22 minutes, or until a toothpick inserted in the center comes out clean. Muffins should be golden and springy to the touch.

Cool:
Let cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

Serve:
Enjoy warm or at room temperature, plain or with butter, honey, or cream cheese.