Boil the pasta in salted water as usual and allow to drain. Wash and halve the tomatoes. Cut the spring onions into rings.
Heat 2 tablespoons of fat in a small saucepan. Stir in the flour and sweat for 1 - 2 minutes. Add 200 ml of water and the milk and bring to the boil while stirring. Stir in the broth and let the sauce simmer for 5 minutes.
Meanwhile, grate the parmesan. Stir 2/3 of it into the sauce, season with salt, pepper and nutmeg. Roast 2 tablespoons of fat and breadcrumbs until golden brown.
Mix the pasta and spring onions and distribute in a greased baking dish. Pour the cheese sauce over the pasta. Cover the casserole with cherry tomatoes and sprinkle with the breadcrumbs and the rest of the parmesan. Bake in the preheated oven at 175 ° C (convection) for about 15 minutes.