Preheat oven to 375°F (190°C). Line a muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, mix the milk, coffee, oil, eggs, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined. Fold in chocolate chips if using.
Divide the batter evenly among the muffin cups.
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Let cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.