Heat oven to 350 degrees. Spray bottom and sides of 13 x 9-inch pan with cooking spray.
In large bowl, stir cookie base ingredients until soft dough forms. Press dough in bottom of pan. Set aside.
In large bowl, beat cream cheese, granulated sugar, 1/4 cup butter, the flour, 1 teaspoon vanilla and the egg with electric mixer on medium speed until smooth. Stir in 1/4 cup pecans. Spread over cookie dough base. Sprinkle with chocolate chips.
Bake 26 to 28 minutes or until filling is set. Sprinkle evenly with marshmallows. Bake 2 minutes longer.
In 2-quart saucepan, melt 1/2 cup butter over medium heat. Stir in cocoa and milk. Heat to boiling, stirring constantly. Remove from heat. With wire whisk, gradually stir in powdered sugar until well blended. Stir in 1 teaspoon vanilla and 1 cup pecans. Immediately pour over marshmallows, spreading gently to cover. Cool 30 minutes.
Refrigerate about 2 hours or until chilled. For bars, cut into 6 rows by 4 rows. Store covered in refrigerator.
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