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Line a 9x13 inch pan with aluminum foil. Grease foil. Set aside.
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Beat 1 cup brown sugar, melted butter, eggs, 1 teaspoon vanilla and if desired bourbon at medium speed of an electric mixer until smooth.
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Combine flour, cocoa, and 1/2 teaspoon salt. Gradually add to the brown sugar mixture, beating until blended. Spread into prepared pan.
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Bake at 375 degrees for 15 minutes. Cool on a wire rack.
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Bring 3/4 cup butter, corn syrup, 3 cups brown sugar and remaining 1/2 teaspoon salt to a boil, stirring constantly, until a candy thermometer registers 250 degrees (hard ball stage). Remove from heat; stir in whipping cream and 2 tablespoons vanilla until blended. Stir in pecans. Pour over prepared crust.
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Bake at 375 degrees for 25 minutes. Cool on a wire rack; cover and chill 8 hours.
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Cut into 12 squares; cut each square into 2 triangles. Store in refrigerator.