Mix milk and vinegar. Let it sit for 10 minutes, you will notice the milk has curdled slightly.
While this mixture is resting, line a 12 cup muffin tray with paper muffin liners or spray with nonstick cooking spray.
Preheat the oven to 375°F (or 190°C).
Take dry ingredients (all purpose flour, sugar, salt, baking powder) in a bowl. Whisk till everything is incorporated well.
In another big bowl, add wet ingredients (milk+vinegar mixture, vanilla, oil). Beat it using a wire whisk till everything comes together.
Now add dry ingredients to the wet. Start mixing with a wire whisk and halfway through switch to a spatula to avoid overmixing.
Then add chocolate chips and fold them into the batter.
Divide into the prepared muffin pan.
Now in a small bowl mix sugar and cinnamon powder, sprinkle over the muffins.
Bake into the preheated oven for 19-20 minutes. Or till the toothpick inserted in the center comes out clean.
Let the muffins cool for 5 minutes in the pan itself then transfer to the cooling rack.
Video
Notes
Milk+Vinegar: I have combined both to make homemade buttermilk. If you have store-bought buttermilk ready in your fridge then use that. Make sure milk or buttermilk is at room temperature.
Oil: I recommend using flavorless oil like corn, canola, vegetable, safflower, etc.
Variations: This is a very versatile muffin batter. Skip chocolate chips and topping, you will have the nice vanilla-flavored batter ready. Customize however you like (a few ideas, add dried fruits, nuts, berries, raisins, dates).
Don’t Over-mix: When combined dry and wet ingredients, do not over mix. This is very important to make fluffy and soft muffins. If you overmix, you will get dense, tough muffins.
This is the thick muffin batter, do not tempted to any other liquid into the batter.
Make vegan muffins: substitute the regular milk with any vegan milk and use vegan chocolate chips. Yes, I have tried myself and it works.