Preheat your oven to 425°F. Line a muffin tin with liners.
Add all your dry ingredients - minus the sugar - into a bowl and stir well.
Add in all the wet ingredients - including the sugar - into another bowl and whisk vigorously until well-combined.
Pour the wet ingredients into the dry ingredient and stir until just combined. There should be lots of lumps, and maybe even one or two streaks of flour.
Fold in the chocolate until just combined. You can also gently stir any streaks of flour away, but you still want lots of lumps in the batter.
Evenly divide the batter among the muffin tin. Top with more chocolate, if desired.
Bake for 5 minutes, then turn down the temperature to 350°F without opening the oven door. Bake for another 14 - 16 minutes, or until a toothpick comes out clean or with a crumb or two attached.
Notes
Gently fold the wet ingredients into the flour. The more you mix, the tougher the muffins will be. For tender, melt-in-your-mouth muffins, you want to just barely combine the wet and dry ingredients.