Heat butter and olive oil in a large sauté pan on medium heat and add the shallots. Stir occasionally for 15-20 minutes until starting to caramelize.
While the shallots are cooking set out a large pot for cooking the pasta, fill with at least 4 quarts of water and add one and a half to two tablespoons of Kosher salt. Bring to a boil and cook the pasta until al dente, according to package directions. Reserve a cup and a half of the pasta water, drain the pasta. Set pasta back in pan off the heat (or in a separate bowl) and mix with the one-fourth of a cup of Meyer lemon juice.
In a separate bowl mix together the mascarpone, parmesan, remaining ¼ cup of Meyer lemon juice, Meyer lemon zest, salt, pepper, red pepper flakes and nutmeg.
When the shallots are almost caramelized, about 20 minutes into cooking, add in the garlic and stir for a minute. Then add in the white wine and cook until reduced slightly. Then add in the mascarpone mixture and stir until heated through. Add the pasta and stir to coat the noodles, adding in the reserved pasta water a few tablespoons at a time until the sauce is creamy but not too thin. You probably won’t use the entire cup of water
Add in the parsley and hazelnuts, reserving a dew teaspoons for garnish, and stir. Divide amongst plates and top with the remaining hazelnuts, parsley, and some freshly grated parmesan. Can add more red pepper flakes too if desired.