Bring 100 ml water to the boil, add frozen spinach, cover and allow to defrost according to package instructions and cook.
Peel, clean and wash the carrots and celery. Clean and wash leek. Cut vegetables into fine cubes. Peel onion and garlic. Dice onion finely, chop garlic. Wash basil, shake dry and cut the leaves into fine strips.
Heat 2-3 tablespoons of oil and fry the minced meat for 5-6 minutes, turning it well. Add the vegetables, approx. 2/3 onion and garlic each, stir in the tomato paste and steam for 4-5 minutes. Season with salt and pepper.
Sprinkle with 1 tbsp. flour and sauté briefly. Add 250 ml broth, tomatoes and oregano. Bring to the boil while stirring, crushing the tomatoes. Simmer sauce for about 5 minutes while stirring. Season to taste with salt and pepper, stir in basil.
For the béchamel sauce, melt the fat in a saucepan. Dust with 3 tbsp. flour and sauté. Add 500 ml broth and milk while stirring. Bring to the boil, simmer for about 5 minutes while stirring. Season to taste with salt, pepper and nutmeg.
Drain the spinach well on a sieve. Heat 1 tablespoon of olive oil in a saucepan, sauté the remaining onions and garlic. Add spinach, heat briefly and season with salt, pepper and nutmeg.
Grate the gouda and parmesan. Cut mozzarella into small cubes.
Grease an ovenproof dish (approx. 28 x 20 cm, 9 cm high). Spread some béchamel sauce thinly on the bottom of the dish. Place 4 lasagne plates on top. Spread a good 1/3 of the chopped sauce on top and cover with 4 lasagne sheets.
Spread with some béchamel sauce and spread the spinach on top. Sprinkle another thin layer of béchamel sauce and cover with 4 lasagne sheets. Spread a good 1/3 of the chopped sauce on top and place 4 lasagne dishes on top.
Spread with the remaining light sauce, add the remaining minced meat sauce in blobs. Sprinkle with cheese. Bake in a preheated oven, 2nd rail from below (electric oven: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 1 hour until golden brown.