While pasta cooks, melt butter in a large pot. Add cream and bring to a simmer. Add mascarpone and stir until melted and smooth. Add salt, pepper, hot sauce (if using) and cheddar; stir until melted and smooth.
Drain pasta, reserving some of the pasta cooking water. Add hot pasta to cheese sauce and stir until coated. If it seems too thick, add pasta water, 1 tbsp at a time, until desired consistency achieved. Serve at once.