We took this super easy one-pot brownie recipe and enhanced it with duck eggs (prized for their richness) and cultured market butter. Regular chicken eggs work well too, just use five instead of four. Twin Post Farm has duck eggs (Dupont); Clear Spring Creamery (Downtown Silver Spring and Dupont) and Blue Ridge Dairy (Dupont) both have amazing butter.
Makes 24 brownies
Position a rack in the center of the oven and heat the oven to 325°F. Line the bottom and sides of a 9x13-inch straight-sided metal baking pan with heavy-duty aluminum foil, leaving about a 2-inch overhang on the short sides. Lightly butter the foil.
Put the butter in a large (4-quart) saucepan over medium-low heat and stir occasionally until melted, about 2 minutes. Off the heat, whisk in the cocoa powder until smooth, 1 minute. Switching to a wooden spoon, add the sugar and salt, and stir until blended. Test check the temperature of the batter—it should be warm, not hot. If it’s hot, wait a few minutes before proceeding.
Stir in the eggs, two at a time, until just blended. Stir in the vanilla until the batter is well blended. Sprinkle the flour over the batter and stir until just blended.
Scrape the batter into the prepared pan and spread evenly. Scatter the chocolate on top. Bake until a toothpick inserted in the center comes out with small bits of brownie sticking to it, about 35 minutes, perhaps a few minutes longer. The key to fudgy brownies is to under-cook them ever so slightly. Cool the brownies completely in the pan on a rack, about 3 hours.
When the brownies are cool, use the foil overhang to lift them from the pan. Invert onto a cutting board and carefully peel away the foil. Flip again and cut into 24 squares. Wiping your knife frequently with a damp cloth helps with slicing.