Gently clean the mushrooms with a soft brush or damp cloth. Slice the caps and dice the stems. If using dried porcini, soak them in warm water for 20 minutes, then chop and reserve the strained soaking liquid.
In a large sauté pan, heat olive oil over medium heat. Add shallots, garlic, rosemary, sage, and half the parsley. Sauté for 3-4 minutes until fragrant.
Add the diced mushroom stems (and soaked porcini, if using). Cook for 1 minute, then add the diced tomatoes. Season with salt and pepper.
Simmer the sauce gently for 20 minutes, stirring occasionally. Add the sliced mushroom caps and continue to simmer for another 10 minutes. Add a splash of mushroom soaking liquid or a little water if the sauce looks too thick.
For a creamy boscaiola, stir in the heavy cream just before finishing and simmer for 2 more minutes. Taste and adjust seasoning as needed.
While the sauce simmers, bring a large pot of salted water to a boil. Cook the pappardelle until al dente, then drain, reserving a small cup of pasta water.
Add the drained pasta to the sauce. Toss gently over low heat, adding a little pasta water if needed for a silky sauce.
Serve immediately, topped with remaining parsley and freshly grated cheese.