- 2 sticks (1/2 pound) unsalted butter
- 5 ounces unsweetened chocolate
- 2 tablespoons instant-espresso powder
- 2 cups sugar
- 1 teaspoon pure vanilla extract
- 5 large eggs
- 1 cup all-purpose flour
- 1 tablespoon cinnamon
- 1/2 teaspoon salt
Preheat oven to 350°F with rack in middle. Butter and flour a 13- by 9-inch baking pan.
Melt butter and chocolate with espresso powder in a 3-quart heavy saucepan over low heat, whisking until smooth. Remove from heat and cool to lukewarm. Whisk in sugar and vanilla. Whisk in eggs 1 at a time until mixture is glossy and smooth.
Whisk together flour, cinnamon, and salt, then whisk into chocolate mixture.
Spread batter in pan and bake until a wooden pick inserted in center comes out with crumbs adhering, 25 to 30 minutes. Cool completely before cutting.