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Preheat the oven to 350 degrees F.
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Butter and flour a 12 by 18 by 1 1/2-inch sheet pan.
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Melt together the butter, 1 pound of chocolate chips, and the unsweetened chocolate in a medium bowl over simmering water.
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Allow to cool slightly.
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In a large bowl, stir (do not beat) together the eggs, coffee granules, vanilla, and sugar.
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Stir the warm chocolate mixture into the egg mixture and allow to cool to room temperature.
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In a medium bowl, sift together 1 cup of flour, the baking powder, and salt.
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Add to the cooled chocolate mixture.
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Toss the remaining 12 ounces of chocolate chips in a medium bowl with 1/4 cup of flour, then add them to the chocolate batter.
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Pour into the prepared sheet pan.
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Spoon the peanut butter over the top of the chocolate mixture and using a knife, swirl it through the chocolate mixture.
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Bake for 20 minutes, then rap the baking sheet against the oven shelf to force the air to escape from between the pan and the brownie dough.
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Bake for about 10 to 15 minutes more or until a toothpick comes out clean.
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Do not overbake!
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Allow to cool thoroughly, refrigerate, and cut into large squares.