Preheat the oven to 200ºC/180 ºC fan/Gas Mark 6. Lay the diced pumpkin and whole garlic cloves on a roasting tray, season with salt and pepper and drizzle generously with olive oil. Roast for 30 minutes until the pumpkin is soft and slightly browned. Remove from the oven and mash the pumpkin with the back of a fork, then stir the chopped spinach and leave it to wilt in the heat. Set aside and leave the oven on. 

Whilst the pumpkin is roasting, partially boil the pasta shells in boiling salted water for 5 minutes. Drain and put under cold running water to stop them from cooking further. Drain again and set aside. 

Make the béchamel by melting half the butter in a saucepan and stirring the flour. Turn up the heat until the buttery flour (roux) turns into a sandy colour. Whisk in the milk and continue to whisk until it is completely incorporated, and the sauce is smooth and slightly thick. Stir in the cream cheese, soup powder and half of the cheese and season to taste. Spread the bechamel into a large ovenproof baking dish and drizzle with olive oil. 

Using your finger, fill each pasta shell with the pumpkin mixture. Press the filled shells into the bechamel in rows. Drizzle with more oil and bake for 30 minutes. Remove from the oven and sprinkle with the remaining cheese. Return to the oven and bake until the top is golden brown. 

While the bake is in the oven, melt the remaining butter in the saucepan and cook until it browns into a nutty colour. Add the rosemary leaves, lemon juice, salt, and pepper. Remove the pasta from the oven and leave to cool for 5 minutes. Drizzle over the rosemary butter and serve.