Warm Toasted Marshmallow S'more Bars

1 pouch (1 lb 1.5 oz) Betty Crocker® sugar cookie mix
1 cup graham cracker crumbs
1 cup butter or margarine, melted
3 cups milk chocolate chips (18 oz)
4 1/2 cups miniature marshmallows

1. Heat oven to 375°F. In large bowl, stir together cookie mix and crumbs. Stir in melted butter until soft dough forms. Press into ungreased 13x9-inch pan.

2. Bake 18 to 20 minutes or until set. Immediately sprinkle chocolate chips over crust. Let stand 3 to 5 minutes or until chocolate begins to melt. Spread chocolate evenly over crust.

3. Set oven control to broil. Sprinkle marshmallows over melted chocolate. Broil with top 4 to 5 inches from heat 20 to 30 seconds or until marshmallows are toasted. (Watch closely; marshmallows will brown quickly.) Cool 10 minutes. For bars, cut into 6 rows by 4 rows. Serve warm. Store any remaining bars tightly covered.