For the cauliflower crust “bread” slices: preheat oven to 220 C / 200 C fan and place a rack in the middle.2
Grease a baking tray and set aside.
In a food processor pulse the cauliflower florets until they resemble couscous.
Transfer the cauliflower to a microwave-safe dish and microwave on high for 8 minutes, until cooked.
Place the cauliflower rice in a tea towel and twist it to squeeze as much moisture as you can. This is very important. The cauliflower rice needs to be dry, otherwise you’ll end up with mushy dough, impossible to use as slices of bread.
Transfer the cauliflower rice to a mixing bowl and once cool, add the beaten egg, mozzarella, ground almonds, salt, pepper and mix well.
Spread cauliflower mixture onto the lined baking sheet and shape into squares.
Place in the oven and bake for about 15 minutes until golden.
Remove and let cool 10 minutes before removing from the tray.
To assemble the sandwich; heat a pan over medium heat. Butter the top side of each slice of cauliflower crust bread. Place one slice of bread in the pan, buttered side down, add the cheese and top with the remaining slice of cauliflower crust bread, buttered side up.
Turn the heat down slightly and cook until golden brown, about 2 to 4 minutes. Gently flip and cook until golden brown on the other side, about 2 to 4 minutes and serve immediately.