Put the spinach and milk in a food processor and blitz until smooth. Add the flour and eggs and blitz again to incorporate. Stir 1 tablespoon of the melted butter through the batter.
Place the frying pan back over a medium–high heat and wipe with a little of the remaining melted butter. Add a ladleful of the batter and swirl the pan until the batter completely coats the base.
Cook the crêpe for 1–2 minutes on one side, then flip over, turn the heat down to low and top with a little of the cheese and ham. Cook for 1 minute before folding in half, then into quarters.
Pop the cooked crêpes into an ovenproof dish and keep warm in the oven at 120°C (225°F), Gas Mark ¼ while you repeat the process with the remaining batter, ham and cheese. Serve the crêpes straight away.