Step 1

Make the ganache: Line a baking sheet with parchment paper. Melt the chocolate over a double boiler.

Step 2

Meanwhile, in a small pot over low heat, combine espresso and cream, and infuse for 4 minutes. Pass infused cream through a fine-mesh sieve.

Step 3

Pour hot cream over melted chocolate and whisk together. Working quickly, pour ganache onto prepared baking sheet and cover with another sheet of parchment. Use your hands to spread ganache evenly between sheets and press to a thickness of 1 inch. Place baking sheet in refrigerator and chill overnight. The following day, cut ganache into 1-inch cubes, working quickly to avoid melting. Place in refrigerator.

Step 4

Make the brownies: Preheat oven to 350 degrees. Butter an 8-by-12-inch rectangular pan and line with parchment paper. In a bowl, combine flour and salt. Set aside.

Step 5

Over a double boiler, melt butter and chocolates, stirring frequently with a spatula. Remove from heat and let cool.

Step 6

Use a stand mixer fitted with paddle attachment or a hand mixer to cream together eggs, sugar and vanilla at medium speed until mixture is pale and foamy and has risen in volume, about 5 minutes. Use a spatula to add a small amount of melted chocolate to eggs to temper them. Add remaining chocolate and gently fold into egg mixture.

Step 7

Add flour mixture, a third at a time, by sifting it over chocolate mixture, folding well between each addition. Add ganache cubes. There should be no streaks in the batter, but avoid overworking it.

Step 8

Transfer batter to prepared baking pan and lightly tap pan on counter to even out batter. Bake, rotating pan halfway through, until batter jiggles evenly, not only in the center, if shaken gently, 18-20 minutes. Place pan on a cooling rack and let cool 1 hour before cutting into squares.