Chocolate marshmallow Brittle

Line the cookie sheet with foil then butter it. Place a single layer of crackers, salted side up, on the sheet. In the pot, bring brown sugar and butter to a boil. Boil 3 minutes, stirring constantly, then remove from heat and add vanilla. Pour butter-sugar mixture over the crackers, sprinkle with 3/4 marshmallow package, and bake at 350 for 5-6 minutes, or until bubbling. Remove from the oven and cover with the chocolate chips (and 1/4 bag left over marshmallow) immediately. Let stand until chips are melted, then spread the chocolate-marshmallow around. Chill until firm, then break into bite sized pieces.