Individually crack four eggs into four individual small bowls. Fill a large pot or saucepan with 1 1/2 liter of water. Add the vinegar and bring to a boil, then immediately reduce the heat to a minimum to a bare simmer. Using a whisk, create a whirlpool, then carefully tip the first two eggs into the water. Cook for 3 - 4 minutes, stirring the water occasionally to prevent the eggs from sticking to the bottom of the pot. But be careful not to touch or stir the eggs. Remove the eggs carefully with a slotted spoon and transfer to a plate lined with a paper towel. Repeat the process with the remaining two eggs.TipOptionally, check the temperature of the water before adding the eggs to the pot of simmering water. The temperature of the water should be 90 °C / 195 °F.Optionally trim off any wispy egg white pieces using kitchen scissors or a knife to ensure a prettier look.
Cut two english muffins in half lengthwise and toast them in an oven, pan or toaster until they are golden brown. Divide between two plates. Place a slice of cooked ham or prosciutto Cotto over each half of the English muffin and carefully place the poached egg on top. Slightly season the egg with salt, then spoon the hollandaise sauce on top. Sprinkle with chopped chives and black pepper. Serve immediately.