Adapted from this recipe on marthastewart.com. Makes 2 dozen brownies.
2 cups all-purpose unbleached flour
1-1/4 tsp baking powder
1 Tbsp instant espresso
1 Tbsp unsweetened cocoa powder
1 tsp kosher salt
2-5/8 sticks (10.5 oz) butter, cut into small pieces (I use Kate's sea salted butter)
11.5-oz bag semi-sweet chocolate chunks (I use Nestle's Toll House chunks), divided
2-3/4 cups granulated sugar
4 large eggs
2 tsp pure vanilla extract
Preheat oven to 350°F.
Prepare an 11x17 rimmed sheet pan: Spray the pan with cooking spray. Line with parchment paper, and spray the paper. Set aside.
In a large mixing bowl, combine the flour, baking powder, salt, instant espresso and unsweetened cocoa. Whisk to combine, and set aside.
In a heatproof bowl (glass or stainless steel work well) set over a pot of simmering water, heat the butter and 7 oz of the chocolate chunks, until almost melted. Remove from heat, and whisk until the mixture is smooth and cooled slightly.
Transfer the chocolate mixture to the bowl of a Kitchenaid-type stand mixer fitted with the whisk attachment. Add the sugar, and beat on medium speed for 3 minutes, until the mixture is smooth (it will still be grainy; don't worry). Beat in the eggs, 1 at a time, and then add the vanilla. Beat on medium speed for 3 minutes (set a timer).
Reduce mixer speed to low, and slowly add the flour mixture. Beat until just incorporated. Remove the bowl from the mixer, and with a rubber spatula stir in the remaining chocolate chunks.
Pour the batter into the prepared sheet pan, and use the rubber spatula to spread as evenly as possible. Bake at 350F for 20-22 minutes. The brownie will have just set, but will still look and feel soft.
Set the pan on a wire rack, and cool completely, 1 hour or more. Cut into 24 large squares. Give away as many as you can, because you will eat the rest. I know.