Set your oven rack to the middle position and heat the oven to 300 degrees. Line a rimmed baking sheet with aluminum foil.
4 English muffins or other rolls, split open, Condiments of your choice
Toast the English muffins or rolls in the toaster (you might need to do this in batches). Transfer them to the foil-lined baking sheet with the insides facing up. Use a butter knife to spread the tops and bottoms with your favorite condiments, if you like. (Ask your diners what they’d like on their sandwiches; if they place different orders, you can use a marker to write each person’s name on the foil next to their sandwich to keep track of whose is whose.)
4 large eggs, 2 cups baby spinach, ⅓ cup water, ¼ teaspoon table salt
Add the eggs, spinach, water, and salt to a blender jar. Place the lid on the blender and hold it in place with a kitchen towel. Blend the mixture until smooth, about 30 seconds.
Use a liquid measuring cup to measure out ½ cup of the egg mixture from the blender.
2 tablespoons unsalted butter, cut into 4 pieces
In a 10-inch nonstick skillet, melt one piece of butter over medium heat until it’s melted and bubbling, 2 to 3 minutes. Carefully pick up the skillet and swirl to coat the pan with an even layer of melted butter.
2 square slices deli American or cheddar cheese, cut in half
Working quickly, pour the ½ cup of egg mixture into the skillet and swirl and shake the pan to coat the bottom in an even layer. Let the eggs cook until set, about 1 ½ minutes. Place a half-slice of cheese (if using) in the middle of the eggs.
Use a plastic spatula to loosen the edges of the eggs from the pan. Working quickly, fold the bottom side of the eggs over toward the middle (covering the cheese, if you’re using it). Repeat folding three more times from the left, top, and right, going around the circle and turning it into a square.
Let the egg square cook for 30 more seconds. Turn off the stove and slide the skillet to a cool burner. Use the spatula to transfer the egg square to one of the toasted English muffin bottoms.
Repeat steps 4-8 to cook the remaining eggs with the remaining butter in three more batches, so each English muffin bottom has an egg square. Turn off the stove.
4-8 slices deli ham
Top each egg square with 1-2 slices of ham and the English muffin top.
Place the rimmed baking sheet with the sandwiches in the oven. Bake until warmed through, about 10 minutes. (This ensures all four sandwiches will be hot to serve at the same time!)
Use oven mitts to remove the baking sheet from the oven and place it on the stovetop or a cooling rack. Use the spatula to transfer each sandwich to a serving plate. Serve.