Fill the 5-quart / 4.7 L pot with 3 L of water, add the salt, and bring to a boil over high heat, about 8 minutes. While it heats, shred the cheddar and grate the Parmesan.
Cook the macaroni for 1 minute less than the package time, usually 7 to 8 minutes, until al dente. Scoop out 60 ml of the pasta water, then drain the pasta and leave it in the colander.
While the pasta cooks, blend the cottage cheese, milk, Parmesan, Dijon, garlic powder, paprika and pepper in the 1.5 L blender for 45 seconds. Scrape the sides once, until no curds are visible.
Return the empty pot to the burner on the lowest heat and melt the butter. Pour in the blended sauce and stir for 2 minutes until steaming, with no bubbles at the edge. If it bubbles, pull the pot off the heat, because boiling makes the sauce grainy.
Add the cheddar a handful at a time, stirring until each addition melts. Fold in the drained macaroni and loosen with the reserved pasta water, 1 tablespoon at a time, until the sauce coats the pasta. Taste for salt and serve within 10 minutes.