- 1 cup (2 sticks) unsalted butter, room temperature, plus more for pan
- 1 1/4 cups all-purpose flour (spooned and leveled), sifted, plus more for pan
- 1 cup granulated sugar
- 1 teaspoon pure vanilla extract
- 5 large eggs, room temperature, lightly beaten
- 1/2 teaspoon coarse salt
- 1/4 cup unsweetened cocoa powder
- 6 ounces semisweet chocolate, chopped or chips
- Preheat oven to 350 degrees. Lightly butter and flour a 4 1/2-by-8 1/2-inch loaf pan. In a large bowl, using an electric mixer, beat butter and sugar on medium-high until very light and fluffy, 7 minutes. Scrape down bowl and beat 1 minute more. Add vanilla, then gradually add eggs, beating well and scraping down bowl as needed. With mixer on low, add salt, then gradually add flour and cocoa powder, beating well to combine and scraping down bowl as needed. Fold chocolate into batter.
- Transfer batter to pan and bake until a toothpick inserted in center of cake comes out with a few moist crumbs attached, 65 minutes. Let cool in pan on a wire rack, 1 hour. Remove cake from pan and let cool completely on rack before slicing.
Let refrigerated butter sit at room temperature for 30 minutes; it should hold an indentation when pressed. If your eggs are cold, submerge them in warm water for 15 minutes.