Preheat oven to 180 C / 350 F. Line a 2 litre bread pan with baking paper. Set aside.
Melt 15 grams butter in a skillet and sauté 1 onion, finely chopped, until softened (a few minutes). Add 1 tsp smoked paprika and sauté a further minute.
Mix 500 grams lean steak mince, 75 grams fresh breadcrumbs, 1 garlic clove, 4 tbsp tomato puree, a handful fresh chopped herbs, 1 free-range egg, beaten, and onion mixture together in a large bowl using your hands to combine thoroughly. Season well with Shetland sea salt and freshly ground black pepper.
Wash and chop 120 grams spinach, removing any tough stalks. Cook in a dry pan until wilted. Drain excess liquid if required.
Lay out a sheet of greaseproof paper on your work surface.
Press meat out into a rectangle the length of you bread pan and 1/2 inch thick.
Sprinkle with a layer of chopped cooked spinach and then with 150 grams mozzarella cheese, torn roughly. Season well with Shetland sea salt and freshly ground black pepper
Using the greaseproof paper to help. start rolling along the short side of the rectangle. Press into shape as you roll.
Close both ends of the meatloaf by firmly pressing the edges together.
Place the meatloaf in the bread pan and cover tightly with tin foil so that no moisture can escape.
Place tin in a large casserole pan filled with 1 inch of water.
Bake for 90 minutes. Remove the foil and broil for a few minutes under a high heat if you want to crisp up the top.
Serve with creamed potatoes and extra veg. Leftovers (if there are any!) freeze very well.