Spicy Mac and Cheese

unsalted butter

slices white bread, cut into 1/2-inch squares 

Kosher salt 

unsalted butter

Cheddar cheese, shredded 

Colby cheese, shredded 

pepper Jack cheese, shredded 

elbow pasta, cooked until almost al dente 

all-purpose flour

kosher salt 

freshly ground black pepper 

cayenne pepper 

dry mustard powder 

grated nutmeg 

sour cream 

egg, beaten 

grated Vidalia or sweet onion 

heavy cream 

half-and-half