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["Heat oven to 350'F.", "In small saucepan over very low heat, melt peanut butter chips and 3 tablespoons softened butter.", "Remove from heat; cool slightly.", "In large mixer bowl, beat remaining 1/2 cup softened butter and 1 cup sugar until light and fluffy.", "Add corn syrup, egg and vanilla; blend thoroughly.", "Combine 2 cups flour, baking soda and salt; add to butter mixture, blending well.", "Remove 1 1/4 cups batter and place in a small bowl; with wooden spoon, stir in remaining 2 tablespoons flour and peanut butter chip mixture.", "Blend cocoa, remaining 1/4 cup sugar and melted butter into remaining batter.", "Refrigerate both batters 5 to 10 minutes or until firm enough to handle.", "Roll both doughs into 1"" balls; roll in additional sugar.", "Place on ungreased cookie sheet.", "Bake 10 to 11 minutes or until set.", "Cool slightly; remove from cookie sheet to wire rack.", "Cool completely.", "Place 1 marshmallow on flat side of 1 chocolate cookie.", "Microwave at MEDIUM (50%) 10 seconds or until marshmallow is softened; place a peanut butter cookie over marshmallow, pressing down slightly.", "Repeat with remaining marshmallows and cookies.", "Serve immediately.", "Makes about 2 dozen sandwich cookies."]