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Place the butter, granulated sugar, and brown sugar in the bowl of the stand mixer. If it is warm, it will melt the butter and ruin the texture of your cake. Set aside until the mixture cools to room temperature.
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Add the remaining 1 cup water and stir until the mixture is smooth. Pour it over the cocoa and whisk or stir until blended and smooth. Heat 1/2 cup of the water in the small saucepan just until it begins to simmer. Preheat the oven to 350 degrees and position oven racks in the lower and upper thirds. Store any leftover frosting in the refrigerator and rewarm it for ice cream sauce, or scoop it for decadent truffles.ġ/2 cup (2 1/2 ounces) unsifted unsweetened Dutch-process cocoa powderġ/2 cup (4 ounces) plus 1 cup (8 ounces) waterġ 1/2 sticks (6 ounces) unsalted butter, softened (65 to 68 degrees)ģ/4 cup (6 ounces) firmly packed light brown sugarġ/4 cup (1 1/4 ounces) unbleached all-purpose flourĢ0 ounces semisweet or bittersweet chocolate (up to 60 percent cacao), finely choppedĢ 1/2 cups (20 ounces) heavy whipping cream If you're not sure which kind you have, check the ingredient label: Dutch-process cocoa powder contains alkali, whereas natural does not. Be sure to use unsweetened Dutch-process cocoa powder natural cocoa powder will react unfavorably with the baking powder. The deep chocolate flavor of this cake comes from the technique of pouring boiling water over cocoa powder, which intensifies and releases all the chocolate notes within.
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