"This has always been a favorite in our family, but you have to have your oven free, and serve immediately after baking. They taste better when they are hot, but even after they have cooled, people will still snatch them up."
Melt cream cheese, Cheddar cheese, butter, and Worcestershire sauce together in top of a double boiler over simmering water, stirring frequently and scraping down the sides with a rubber spatula. Set aside to cool, about 10 minutes.
Beat egg whites in a glass, metal, or ceramic bowl until stiff peaks form; fold into cooled cheese mixture using a rubber spatula. Gently run spatula around the edges of the bowl, lifting the bottom up and over the center until blended.
Line a baking sheet with parchment paper.
Dip bread cubes into cheese and egg white mixture, coating thoroughly. Place on lined baking sheet and refrigerate, 8 hours to overnight.
Preheat oven to 400 degrees F (200 degrees C).
Bake in the preheated oven until golden, 10 to 12 minutes.
If you are having more than 6 people over, I would make a batch to freeze and another to store in the refrigerator overnight. Make sure cheese squares are completely frozen before placing them in a resealable plastic bag. Thaw before baking.
Per Serving: 532 calories;34 g fat;
40.4 g carbohydrates;
16.4 g protein;
98 mg cholesterol;
870 mg sodium.