Instructions: Preheat oven to 325 degrees. Butter baking pan, line it with aluminum foil, and butter the foil.

Put butter and sugar in a large bowl and blend until smooth using electric mixer on medium speed. Beat in peanut butter until smooth.

Stir egg and vanilla together in a bowl and add to peanut butter mixture until combined. In a small bowl, whisk together flour, baking soda and salt. Add to butter mixture and combine well. Stir in 1 portion each of white and semisweet chocolates and combine. Add 1 portion of pecans and mix until combined.

Spread batter evenly in prepared pan and bake for 30 to 35 minutes, or until center is soft but no longer runny. Remove pan from oven and immediately sprinkle remaining white and semisweet chocolates over top. Cover pan with aluminum foil and set aside to let chocolates melt.

When melted, swirl chocolates together with tip of a sharp knife to make a marble-ized effect. Sprinkle remaining pecans over top. Let bars cool completely in pan on a wire rack. To serve, cut into 2 inch squares and arrange on a serving plate.

Note: These are great right out of the oven with a scoop of ice cream for dessert. If you are giving them as cookies, you might want to cut the bars smaller, since these are incredibly rich. Also, for neater cookies, refrigerate the pan for a few hours before cutting into bars.

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