Heat the oven to 375°F. Place one rack in the lower third and another rack in the upper third of the oven.
Whisk the eggs together with the milk and salt in a large mixing bowl. Film a 9x13 baking pan with cooking spray, and pour the eggs into the pan. Place on the lower rack in the oven. Bake until the eggs are puffed around the edges with golden spots, and a paring knife inserted in the middle comes out clean, 25 to 30 minutes. Cool completely.
Line a baking sheet with foil. Lay the bacon on the baking sheet in a single layer with no pieces overlapping. Turn up the edges of the foil to catch the grease. Place the bacon on the upper rack in the oven and bake until the bacon is crispy, 15 to 20 minutes.
When the eggs and the bacon are both finished, place the English muffins cut-side-up on a baking sheet and toast in the oven for just a few minutes, until the edges are toasted. If desired, you can brush the muffins with butter before toasting.
Use a spatula to lift the eggs out of the pan and onto a cutting board. Using a large biscuit cutter or drinking glass (roughly the same size as your English muffins), cut rounds out of the eggs. Use the scraps to assemble even more, if desired.
Lay the bottom halves of the English muffins in a row on your counter. Top each one with an egg round, a slice of cheese, and 2 pieces of bacon (if using). Finish by adding the muffin tops.
Wrap each sandwich in a square of aluminum foil. Use a permanent marker to write the contents and date on the sandwich. Put all the sandwiches in a freezer bag or container. Sandwiches freeze for up to 1 month, or keep in fridge for three days.
Reheating instructions from refrigerator: Unwrap the cold sandwich from the tinfoil and wrap in a paper towel. Heat at full power in microwave for 45 seconds.
Reheating instructions from freezer: Same as above but for 1-1/2 minutes.
