Preheat your grill or oven to 350-400F. Grease an 8-inch cast-iron skillet with 1 tablespoon melted butter.
In a small bowl, whisk together cornstarch, cocoa powder, and salt.
In a large microwave-safe bowl, microwave 6 tablespoons butter and 1½ cups of chocolate in 30-second increments, stirring each time, until melted and smooth, about 2 minutes. Let cool for 5 minutes.
Whisk in the sugar and vanilla. Mix in the eggs, one at a time, until combined. Add the cornstarch mixture and stir vigorously until the mixture is smooth, about 2 minutes.
Stir in ¼ cups chocolate chips and the pecans.
Pour the batter into the skillet and smooth the top. Sprinkle the remaining ¼ cup of chocolate chips on the top.
Grill, covered, until a tester pick inserted in the middle of the brownies comes out with a few crumbs, 35 to 40 minutes. Check every 5 minutes after 30 minutes. If baking in the oven, bake for 35 minutes. Remove from heat and let cool in the skillet.