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["Put oven rack in middle of oven; set to 325u00b0F.", "Construct a foil sling: Cut one 18"" length foil and fold it lengthwise so that it is 8-inches wide.", "Fit foil into length of 9x13-inch baking dish, pushing it into corners and up sides of pan; allow excess to overhang pan edges.", "Cut one 14-inch length foil and, if using extra-wide foil, fold it lengthwise so that it is 12"" wide; fit into width of baking pan in same manner, perpendicular to first sheet.", "Spray foil-lined pan with nonstick cooking spray.", "Whisk together flour, salt, and baking powder in medium bowl; set aside.", "Melt chocolate and butter in large heatproof bowl set over saucepan of almost-simmering water, stirring occasionally, until smooth.", "(Alternatively, in microwave, heat butter and chocolate in large microwave-safe bowl on high for 45 seconds, then stir and heat an additional 30 seconds. Stir again, and, if necessary, repeat in 15-second increments; do not let chocolate burn.) When chocolate mixture is completely smooth, remove bowl from saucepan and gradually whisk in sugar.", "Add eggs, one at time, whisking until thoroughly combined after each addition.", "Whisk in vanilla.", "Add about one third of flour mixture and fold with rubber spatula until almost fully incorporated; repeat with half of remaining flour, then all of remaining flour, folding until batter is completely smooth and homogeneous.", "Transfer batter to prepared baking pan; using spatula, spread batter into corners of pan and smooth surface.", "Bake until toothpick or wooden skewer inserted into center of brownies comes out with few moist crumbs attached, 30 to 35 minutes.", "Cool on wire rack to room temperature, about 2 hours.", "For the frosting: In standing mixer fitted with flat beater, beat butter and confectioners' sugar at low speed until just incorporated, then increase speed to medium and beat until smooth and fluffy, about 1 1/2 minutes.", "Add 1 tablespoon milk and mint extract and continue to beat until combined, about 30 seconds, adding up to 1 additional tablespoon milk if necessary to achieve soft, spreadable consistency.", "Using offset spatula, spread mint frosting evenly onto cooled brownies, cover with foil, and refrigerate until firm, about 1 hour.", "For the glaze: Melt chocolate and butter in medium heatproof bowl set over saucepan of barely simmering water, stirring occasionally, until smooth; set aside to cool slightly, about 10 minutes.", "Pour chocolate glaze on frosted brownies; using offset spatula, spread glaze into even layer.", "Cover with foil and refrigerate until firm, about 1 hour; remove brownies from pan by lifting foil overhang; cut into 2-inch squares and serve.", "(Store leftovers in airtight container in refrigerator)."]
