Prep. Adjust the oven rack to the lower-middle position and preheat the oven to 350º F. Line an 8 x 8 baking pan with parchment paper to easily lift the brownies from the pan for cutting.
Melt the butter, chocolate, and sugar. Add the butter and chocolate bars to a microwave-safe bowl. Heat in the microwave in 30-second intervals until the chocolate has softened. Stir the sugars into the hot chocolate until smooth.
Make the brownie batter. Add the eggs, one at a time, stirring to fully combine into the melted chocolate mixture before adding the next. Continue to stir until the mixture has become smooth and glossy. Stir in the salt, vanilla extract, espresso powder, and flour. Stir until smooth. Pour the batter into the prepared baking dish.
Bake. Bake until the brownies are set and a cake tester or toothpick inserted in the center comes out with wet crumbs, about 30 - 40 minutes. Cool the brownies in the pan on a wire rack for 5 minutes. Then, lift the brownies out of the pan by the edges of the parchment paper and cool on the wire rack.
Serve. Cut the brownies into individual squares and serve. If not serving soon, do not cut the brownies.
Notes
Storage Tips
To store. Store the brownies in an airtight container at room temperature for up to 5 days.To freeze. Freeze brownies for up to 3 months in an airtight, freezer-safe container. Thaw overnight to serve.
Recipe Variations
The Best Gluten-Free Brownies Recipe - Substitute an equal amount of 1:1 gluten-free flour for baking, such as King Arthur Flour Measure for Measure Gluten-Free Flour.The Best Dairy-Free Brownies Recipe - Substitute your favorite dairy-free butter substitute for the butter in this recipe.*Note: The results in the texture and consistency of the baked brownies may differ with ingredient substitutions.