18tablespoons (9 oz;270g)unsalted butter at room temperature
¾cup (140g)dark muscovado sugar
¾cup (125g)light brown sugar
12ounces (400g)semi-sweet chocolate, preferably Valrhona, Lindt, or Scharffenbergercoarsely chopped
Preheat the oven to 375°F (190°C). Line several baking sheets with parchment paper.
Sift together all the dry ingredients onto a piece of waxed or parchment paper.
In a large bowl or the bowl of an electric mixer, mix the butter until it is light and pale yellow. Add the sugars and mix until thoroughly combined and light. Add the eggs, one at a time, just until thoroughly combined. With the mixer running slowly, add the vanilla, then the dry ingredients, mixing just until combined. Finally, with the mixer running slowly, add the chocolate. You may need to finish mixing in the chocolate by hand so that it is thoroughly mixed throughout the dough.
Scoop out heaping tablespoons of dough, and place the mounds 1-1/2 inches (2.75cm) apart on the prepared baking sheets. Bake in the center of the oven 12 to 15 minutes, depending on whether you like your cookeess soft, or fully baked!