Heat oven to 375°F. In ungreased 1-quart casserole, mix hot water, milk, 2 tablespoons butter and the mashed potato mix. Cover with plastic wrap, turning back one side to vent steam. Microwave on High 2 to 4 minutes or until moistened.
Whip potatoes with fork until fluffy; stir in chives. Smooth top of potato mixture with rubber spatula.
Crush crackers. In small bowl, mix crushed crackers, cheese and 2 tablespoons melted butter; sprinkle over top of potatoes.
Bake 10 to 15 minutes or until potatoes are hot and topping is crisp.