Soak the dried mushrooms in the hot water in a small bowl.
Add 1 Tbs. salt to 2 gallons water in a large pot and put over high heat to boil.
While the water is heating, melt the butter in a very large skillet over medium heat. Stir in the flour, 1/2 tsp. salt, and pepper and simmer over low heat for 2 minutes. Remove from the heat and whisk in the cream a little at a time and then the milk. Heat over medium heat, stirring constantly, until smooth. Remove from the heat. Sprinkle the lemon juice over the mozzarella, toss with a fork to mix, and then whisk the mixture into the sauce.
Stir the red pepper flakes into the olive oil in another large skillet over medium heat. Stir in the sliced mushrooms and the ham. Sauté briefly and remove from the heat. Lift the dried mushrooms out of the bowl with a slotted spoon and stir into the mushroom mixture.
Decant and add all but the last tablespoon of the soaking liquid. Add the tomatoes and stir into the mozzarella sauce.
Stir the fettuccine into the boiling water and continue stirring for the first 2 minutes of cooking. Cook for the amount of time recommended on the package. Reheat the sauce. Drain the pasta and stir into the skillet with the sauce. Cover and let stand for 1 minute. Serve immediately.