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1
Preheat the oven to 350 degrees F. Grease a 9 by 13-inch baking dish with 1 tablespoon of the butter.
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2
Sprinkle 1 tablespoon of flour into the pan to coat the sides and bottom, knocking out any excess.
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3
Set aside.
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4
In the top of a double boiler or in a bowl set over simmering water, combine the remaining 12 tablespoons butter and the chocolate.
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5
Cook, stirring, until smooth, about 3 minutes.
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6
Add the granulated sugar and whisk until smooth.
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7
Add 1/4 cup of the flour and whisk to combine.
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8
Alternate adding the remaining flour and eggs, whisking well after each addition.
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9
Stir in the toasted nuts and vanilla.
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10
Pour into the prepared pan, shifting the pan to create an even layer.
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11
Bake until risen and a toothpick inserted in the center comes out clean, about 30 minutes.
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12
For the Fudge Topping: While the brownies are in the oven, in a medium saucepan, combine the butter, cocoa powder and buttermilk over medium heat.
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13
Cook until the butter melts and mixture just comes together.
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14
Remove from the heat and whisk until smooth.
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15
Sift the confectioners' sugar into a medium bowl.
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16
Add the chocolate mixture and vanilla and whisk until smooth.
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17
Remove the brownies from the oven and, with the handle of a wooden spoon, poke holes into the brownies every 1 to 2 inches.
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18
Pour the Fudge Topping over the brownies and smooth with a rubber spatula.
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19
Let cool on a wire rack for at least 1 hour before cutting.
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20
Cut into 2-inch brownies and serve.
