Ingredients
Method
Preheat oven to 375°. Lightly coat a metal 8x8" baking pan with nonstick vegetable oil spray or unsalted butter, room temperature, then line with parchment paper, leaving generous overhang on 2 sides. Lightly coat parchment with nonstick spray.
Whisk 62 g (½ cup) all-purpose flour, 50 g (½ cup) Dutch-process cocoa powder, and 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt in a small bowl to combine.
Combine ½ cup (1 stick) unsalted butter and 113 g (4 oz.) bittersweet chocolate, preferably 70%, broken into pieces, in a medium metal bowl set over a large saucepan of barely simmering water (bottom of bowl should not be touching water). Heat, stirring occasionally, until chocolate is melted and smooth, about 5 minutes.
Whisk in 250 g (1¼ cups) granulated sugar, then add 3 large eggs one at a time, whisking very vigorously between additions. Once all eggs are incorporated, continue to whisk 1 minute more. Remove bowl from heat and whisk in 1 Tbsp. vanilla extract, then whisk in dry ingredients. Using a rubber spatula, stir in 113 g (4 oz.) semisweet chocolate chips. Scrape batter into prepared pan; smooth surface.
Bake brownies until set across top and a tester inserted into the center comes out with just a few moist crumbs attached, 27–30 minutes. Let cool in pan at least 30 minutes, preferably in refrigerator, before cutting into 12 pieces. Do ahead: Brownies can be baked 4 days ahead. Store tightly wrapped at room temperature.