Make the easy "hollandaze": Place the egg yolks, lemon juice, mustard and hot sauce in a blender and blend until just combined, about 1 minute. While the blender is still running, slowly stream in the melted butter through the top hole until the sauce thickens, about 15 seconds. Adjust the seasoning with more lemon juice and some salt. Cover and keep warm (you can also transfer to a Thermos).
Make the sandwiches: Heat a large nonstick skillet over medium heat; add 1 tablespoon butter and let melt. Fry the ham until slightly charred, 2 to 4 minutes per side. Wipe the skillet clean and add the remaining 1 tablespoon butter. When the butter is melted, fry the eggs over-easy, 1 1/2 to 2 minutes per side; season with salt and pepper.
Toss the baby spinach, lemon juice, and salt and pepper to taste in a small bowl. Pile some of the dressed spinach on the bottom of each English muffin. Top with a piece of ham, then slide 1 fried egg on top of each. Ladle some of the hollandaze sauce on top, close the muffins and serve.