If using uncooked bacon heat a tablespoon of oil in a large frying pan over a medium heat. Add the bacon and cook for 2-3 minutes. Add the mushrooms, thyme leaves and garlic. Sauté for 5-6 minutes until the mushrooms are golden.
Meanwhile cook the pasta as per packet instructions.
While the pasta is cooking mix together the egg yolks, cream and cheese in a bowl.
Drain the pasta, reserving about 120ml of the liquid. With the saucepan off the heat, return the pasta to it along with the reserved water, bacon/cooked ham and egg, cream and cheese mixture.
Return to a very low heat and stir constantly for a minute or two until the sauce thickens. Taste and season if necessary.
Divide between four bowls and sprinkle over some thyme leaves and more cheese if you wish.
Serve with a fresh green salad and some crusty bread