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1
Center a rack in the oven and preheat the oven to 350 degrees F.
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Butter a 9x13 inch baking pan, line it with wax paper or parchment paper and butter the paper.
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Put the pan on a baking sheet.
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4
To Make the Brownie Batter:
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Put both chocolates and the butter in a bowl set over a saucepan of simmering water.
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Stirring occasionally, heat just until the ingredients are melted, shiny and smooth.
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If the mixture get too hot, the butter will separate from the chocolates. Remove the bowl from the heat.
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8
Working with a stand mixer, preferably fitted with a paddle attachment, or with a hand mixer in a large bowl, beat the sugar and eggs on medium-high speed for about 2 minutes, until pale, thick and creamy.
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Beat in the salt and vanilla extract. Reduce the speed to low and mix in the melted chocolate and butter, mixing only until incorporated.
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Scrape down the sides of the bowl with a rubber spatula, then, still on low speed, add flour, mixing only until it disappears into the batter.
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Using the spatula, fold in the walnuts, and scrape the batter into the prepared pan.
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Set aside.
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13
To Make the Cookie Dough:
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Whisk together the flour, baking soda and salt.
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Working with the stand mixer in the cleaned bowl or with the hand mixer in another large bowl, beat the butter and both sugars together on medium-high speed until smooth and creamy, about 3 minutes.
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One at a time, add the egg and the yolk, beating for 1 minutes after each addition.
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Beat in the vanilla.
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Reduce the mixer speed to low and add the dry ingredients, mixing only until they disappear into the dough. Still on low, mix in the chopped chocolate.
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Drop the cookie dough by spoonfuls over the brownie batter and, using a spatula and a light touch, spread it evenly over the batter.
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Bake for 50-55 minutes, or until the cookie top is deep gold brown and firm and a thin knife inserted into the brownie layer comes out with only faint streaks of moist chocolate.
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Transfer the pan to a rack and cool to room temperature.
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22
Before I baked these I read some reviews. The brownie layer tends to be under baked while the cookie layer comes out perfectly. Some people suggest that you bake the brownie layer for 15 minutes at 350F. before proceeding. I made mine this way and they were fine. *
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23
When the brownies are completely cook, carefully run a knife between the sides of the pan and the brownies, then invert them onto another rack, remove the paper and turn the right side up onto a cutting board.
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24
Cut into bars about 2 inches x 1 inch. (You can cut larger bars if you're serving cookie lovers with Texas-size appetites.)
