1/4 cup butter or margarine, divided
HEAT oven to 350°F.
MELT 3 Tbsp. butter in medium saucepan on medium heat. Whisk ; cook 2 min., stirring constantly. Gradually stir in milk. Bring to boil; cook and stir 3 to 5 min. or until thickened. Add VELVEETA; cook 3 min. or until melted, stirring frequently. Stir in macaroni.
SPOON into 2-qt. casserole sprayed with cooking spray; sprinkle with Cheddar. Melt remaining butter; toss with Ritz cracker crumbs as well as the diced lobster meat. Sprinkle over casserole.
BAKE 25 min. or until heated through.