Cut crust off all sides of bread. Cut into 1-1/2-in. cubes; set aside. In a large saucepan, melt butter. Stir in cream cheese until melted. Remove from the heat; stir in cheddar cheese and blue cheese until melted.
Preheat oven to 375°. In a small bowl, beat egg whites until stiff peaks form. Fold into cheese mixture. Dip bread cubes into cheese mixture, turning to coat.
Place on greased baking sheets; sprinkle with paprika. Bake 12-15 minutes or until bottoms are golden brown. Serve warm.
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