1. Heat Président unsalted butter in a pan over a low heat. Once melted, add the spring onion and garlic and cook for 2 mins until softened. Throw in the spinach, then turn up the heat a little and cook until the spinach has wilted and any liquid dissolved. Stir in the double cream, Dijon mustard and 75g of Président grated emmental. Cook for 2 mins until the cheese has melted. Season as desired, remove from the heat and set aside.
2. Heat a grill on high and toast the croissants until the outside is just golden. Once lightly toasted, turn them over so the sliced side is facing up. Spoon the cheese and spinach mixture over them, then top with the remaining cheese. Return to the grill until the top half of the croissant is golden and the cheese is bubbling. Sandwich together and serve.