First, halve the English muffins and toast them. Set aside.
In a large pot, bring the water and vinegar to a low boil. Crack an egg into a small bowl. Using a slotted spoon, stir the water vigorously to create a vortex, and drop the prepared egg into the center. Keep gently stirring the water as the egg cooks and solidifies. Cook egg for 3 minutes, then remove with the slotted spoon and place on a plate topped with a paper towel. Repeat with all the eggs.
Finally, prepare the hollandaise sauce. In a blender, mix together the egg yolks, lemon juice, and salt and pepper on high until smooth and creamy. As the blender runs on high, slowly drizzle in the melted butter until everything is incorporated, and the sauce is thick and pale yellow.
You're now ready to assemble! On each English muffin half, place some arugula and a slice of prosciutto. Top with an egg and some hollandaise sauce. Serve immediately!