Yield: Makes 32 brownies
1 1/2 sticks (3/4 cup) unsalted butter, divided
5 oz unsweetened chocolate, coarsely chopped
2 cups sugar
1 tablespoon instant-espresso powder or instant-coffee granules
1 teaspoon vanilla
1/2 teaspoon salt
4 large eggs
1 cup all-purpose flour
3/4 cup semisweet chocolate chips
Preheat oven to 375°F. Line a 9" x 12" baking pan with foil, allowing 2 inches of foil to hang over ends of pan, and grease foil well (except overhang) with 1 tablespoon butter.
Melt remaining 11 tablespoons butter with unsweetened chocolate in a large metal bowl set over a pan of barely simmering water, stirring until smooth. Remove bowl from heat and whisk in sugar, espresso powder, vanilla, and salt (mixture will be very thick and grainy), then add eggs 1 at a time, whisking after each addition until batter is smooth.
Toss together flour and chocolate chips in another bowl and add to batter, stirring until just combined.
Spread batter evenly in baking pan and bake in middle of oven until top is firm and edges just begin to pull away from sides of pan, about 23 to 25 minutes (do not overbake).