Preparation:Combine potatoes, onion, salt, & water in a 2 quart glass casserole dish. Cover with glass lid or plastic wrap. Microwave on high for 12 to 15 minutes or until potatoes are tender. Blend flour with 1/2 cup of water to make a smooth paste. Stir in 1-1/2 cups milk. Stir into potato mixture. Continue cooking on high for 4 to 5 minutes until thickened.