How to Make It
Lightly coat the insides of four 8-oz mason jars with cooking spray.
Crack one egg into each jar and top with ¼ tablespoon butter, ¼ cup Fontina, ¼ teaspoon salt, and several grinds pepper. Crack a second egg into each. Screw the lids onto the jars, place in a large saucepan, and pour water into the saucepan until it reaches the top of the eggs, about 2 inches. Allow the water to come to a simmer and cook until whites are set (check by looking through the jars), 7 to 8 minutes. Unscrew the caps and serve with toasted bread.