In a medium saucepan, bring the stock to a simmer over medium heat. Reduce the heat to very low to keep hot.
In a large heavy saucepan, heat the oil and melt the butter over medium-high heat. Add the shallots and garlic, and cook, stirring until fragrant and soft, about 3 minutes. Add the mushrooms and cook, stirring, until wilted and their liquid is evaporated, 4 to 5 minutes. Add the rice and cook, stirring constantly, until the grains are opaque, about 1 minute. Stir in the thyme. Add the wine and cook, stirring, until nearly all evaporated. Add 3/4 cup of the stock, the salt, and pepper. Cook, stirring constantly, until the stock is nearly all evaporated. Continue adding more stock 1/2 cup at a time as the previous addition is nearly absorbed, until the rice is tender and the risotto is creamy, 18 to 20 minutes. Stir in cream, 1/2 cup of the cheese, and the parsley and mix well.
Remove from the heat and adjust the seasoning, to taste. If desired, stir in truffle oil to taste.
Serve immediately, topping each portion with a sprinkling of the remaining cheese and ham.