Preheat the oven to 180℃/350℉ and position a rack in the center of the oven. Line a 12 cup muffin tray with muffin cases.
Whisk together the dry ingredients in a large bowl. In a smaller bowl whisk together the wet ingredients. Fold the wet mix into the dry mix with a spatula until just combined.
Spoon into the muffin cases filling the batter 3/4 of the way (you may have some batter left to make a few extra muffins depending on the size of your muffin cups). Sprinkle the tops with a little raw sugar or demerera sugar and bake in the oven for about 15 minutes, until a skewer inserted into the middle comes out without any raw batter attached (some crumbs are fine).
Remove from the oven and let the muffins sit in the tin for a few minutes before removing to a wire rack to cool. Best eaten suuuuuuper fresh while the chocolate is still melty.