Prep time 30 minutes
3 tbsp. extra-virgin olive oil
150g prosciutto, very finely chopped
2 garlic cloves, minced
750g mushrooms, very finely chopped
2 tbsp. white wine
2 tbsp. chopped flat-leaf parsley
Sea salt and freshly ground black pepper
Ingredients for the white sauce
3 tbsp. butter
Generous ¼ cup plain (all-purpose) flour
Pinch of sea salt
Pinch of grated nutmeg
150g grated Parmesan
Bring a large saucepan of salted water to the boil and cook the conchiglioni until al dente (check the instructions on your packet for cooking time). Drain the pasta, rinse under cold water and let drain upside-down on a large plate or tray, so any excess water drains off.
Heat the olive oil in a frying pan (skillet) over a medium–high heat, add the prosciutto and sauté for 1 minute. Then add the garlic and sweat for 1 minute. Stir in the mushrooms, increase the heat, add the wine and sauté for 5–7 minutes, until the mushrooms are cooked. Remove from the heat, season with salt and pepper, then stir in the parsley and let cool slightly.
Preheat the oven to 180°C fan/200°C/400°F/gas mark 6.
Make the white sauce: melt the butter in a small saucepan, then remove from the heat and, with a small whisk, mix in the flour very quickly to avoid lumps. Gradually add the milk, whisking well between each addition. Return to the heat and cook over a medium heat for 3–4 minutes, whisking all the time, until the sauce begins to thicken. Remove from the heat, season with salt and nutmeg, and stir in half of the grated Parmesan.
Combine a ladleful of the white sauce with the mushroom mixture and mix well. Line the bottom of a large baking dish (about 34 x 22 cm/ 13 x 9 in) with about half of the white sauce. Fill the pasta shells with the mushroom mixture and lay them in the dish on top of the sauce. Pour over the remaining white sauce and sprinkle with the remaining grated Parmesan. Bake in the hot oven for 20 minutes, until golden and bubbly.