1. Rehydrate the mushrooms according to the on-pack instructions.
2. Pre-heat the oven to 180c fan.
3. Cook the pasta 2 minutes less than stated on the pack instructions.
4. Meanwhile, melt 2 tbsp of butter in a saucepan.
5. Add the garlic and mustard powder and cook for 1 minute.
6. Stir in the flour and cook for 1 minute then gradually whisk in the milk.
7. Simmer for 5 minutes, whisking constantly until thickened.
8. Take off the heat and stir in the cheddar and half of the parmesan cheese and the mushrooms.
9. Add the pasta to the sauce and season with salt and pepper.
10. Place into a large oven proof dish.
11. Mix the breadcrumbs and remaining parmesan together and sprinkle over the pasta dish.
12. Bake for 20 minutes until golden.