Bring a saucepan of salted water to the boil, add the macaroni and oil and cook until tender, but still firm to the bite. Drain and return to the pan.
Add 25g of the butter, cover, shake the pan and keep the pasta warm.
Melt the remaining butter in a saucepan and fry the fennel for 3-4 minutes. Stir in the mushrooms and fry for a further 2 minutes and then stir in the sausage and bacon and remove from the heat.
Make bechamel sauce, first melt 25g butter in a saucepan and stir in 25g flour, combine well creating a paste. Gradually sitr in 300ml of warm milk and then add the finely chopped onion, peppercorns and parsley sprigs and season with salt, thyme and grated nutmeg.
Allow to simmer, but constantly stir the mixture for a further 15 minutes before straining.
Stir the meat mixture into the bechamel sauce and pour into a greased ovenproof dish and spread evenly. Sprinkle over the parmesan cheese and arrange the tomato slices in a ring around the edge. brush the tomatoes with olive oil and sprinkle over the oregano.
Bake in a preheated oven at 180°C, gas mark 4 for 25 minutes, or until golden brown. Serve immediately.
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