To prepare the topping, a large bowl combine panko, Gruyere, parmesan, butter, paprika and truffle oil. Mix together until combined and set aside.
Cook pasta in a large pot with salted water until a bit before al dente. Drain and rinse under cool water. Set aside until ready to use.
In a large skillet or cast iron pan, cook pancetta over medium heat until done. Remove to a plate and set aside. Add onion to same skillet and cook until caramelized 5-7 minutes. Add mushrooms and garlic, cook for another 5-7 minutes, adding a bit more butter if needed. When done place in a bowl and set aside. Deglaze pan with 1/3 cup Kunde Chardonnay, add 4 T butter. When melted, add 1/4 cup flour and stir with a wooden spoon until it smells nutty, about 2-3 minutes. Whisk in the milk and bring to a simmer. Keep whisking and cook until slightly thickened, about 5 minutes. Add the cheeses, mustard, cayenne, thyme, salt (1/2 tsp truffle salt optional) and freshly ground pepper, then add the pasta, pancetta and mushrooms. Stir until well combined. Taste and adjust seasoning if needed. If you’re baking in the cast iron pan, add panko topping evenly and bake 20-30 minutes until golden brown on top. Sprinkle sage leaves on top for a pretty presentation.
If you’re using a casserole dish or 9 x 13 inch dish, butter sides and pour the mixture into the dish then evenly cover with topping. Preheat oven to 350 degree. Bake until golden brown on top - 20-30 minutes. Remove from oven and let sit 5-10 minutes before serving. Serves 6-8.