Place a layer of tater tots in the bottom of a large cake pan or casserole dish (you do not have to thaw). Brown and crumble sausage, drain. Mix together eggs, milk, mustard and salt, beat well. Add sausage to egg mixture and pour over tater tots. Let casserole refrigerate overnight. Sprinkle cheddar cheese and/or bacon bits on top. Bake in morning at 350 degrees for 45 minutes. The cheese will melt nicely. Serve hot.