To make the creamed spinach, wash the baby spinach well then place in a bowl.
Cover with boiling water and allow to blanch for a minute.
Drain and squeeze out the excess water (be careful, it will be hot).
Chop the spinach then place in a warm pan. Add the feta cheese and cream and allow to simmer for 5-6 minutes until the cream has reduced.
Season with the lemon, salt and pepper and remove from the heat to cool to room temperature.
When the spinach has cooled down, sandwich a few spoons with the mozzarella between two slices of bread.
Heat a griddle pan over medium-high heat.
Generously butter the top and bottom of the sandwich then place on the grill. Cook for 3-4 minutes, flipping half-way, until the sandwich is golden brown and all the cheese has melted.
Remove and serve.