01 -  Preheat oven to 350°F (175°C) if you'd like to warm the assembled sandwiches. 
 02 -  In a bowl, whisk together the eggs, milk, salt, and pepper. 
 03 -  Heat butter in a skillet over medium heat. Add eggs and scramble until just set. Remove from heat. 
 04 -  Slice croissants in half and lightly toast them if desired. 
 05 -  Assemble each sandwich: bottom half of croissant, slice of cheese, scrambled eggs, cooked bacon or sausage, and any optional toppings. 
 06 -  Top with the other half of the croissant. 
 07 -  If desired, place assembled sandwiches on a baking sheet and warm in the oven for 5–7 minutes to melt the cheese and heat through. 
 08 -  Serve warm.