Heat oven to 375°F. Spray 24 regular-size muffin cups with Crisco® Original No-Stick Cooking Spray. Microwave frozen potatoes as directed on bag. Cool 3 minutes; coarsely chop.
In medium bowl, mix potatoes, ham, mushrooms, 1/4 teaspoon salt and 1/4 teaspoon pepper. In another medium bowl, beat eggs, milk and flour with electric mixer on medium speed until well blended.
Spoon 2 tablespoons potato mixture into each muffin cup. Divide egg mixture evenly among muffin cups (about 3 tablespoons each). Sprinkle with cheese.
Bake 12 to 17 minutes or until center is set. Cool 2 minutes. Run knife around edge of each frittata to loosen; remove to serving platter.