Bring a pot of salted water to a boil. Add the pasta and cook it for 2 minutes less than the cooking time indicated on the package.
While the pasta is cooking, reserve 150 ml of the pasta water before draining.
Heat the olive oil in a large frying pan. Add the onion and sauté for 2 minutes, until softened.
Add the sliced mushrooms and cook over high heat for 6 to 7 minutes, until they are nicely browned and their liquid has evaporated.
Add the minced garlic, thyme, salt, and pepper, and stir well.
In a bowl or measuring jug, combine the CARPOS Oat Drink OLYMPOS and the cornstarch. Mix thoroughly until the cornstarch is completely dissolved.
Pour the mixture into the pan. Add the mustard and nutmeg, then cook for 2
to 3 minutes, stirring continuously until the sauce begins to thicken.
Add the cooked pasta, the Grated Kefalotyri Cheese OLYMPOS, and the reserved pasta water. Cook for another 1 to 2 minutes, stirring, until the sauce is smooth and evenly coats the pasta.
Garnish with chopped parsley, serve immediately, and enjoy!

