The four Roman pastas
They are variations on the same handful of ingredients, and knowing the difference tells you a great deal about the kitchen you are sitting in.
Gricia is the ancestor: guanciale (cured pork cheek), pecorino romano, black pepper. Add tomato and you get amatriciana. Drop the guanciale and keep only cheese and pepper, emulsified with pasta water, and you have cacio e pepe. Add egg yolk to the gricia instead of tomato, and you have carbonara.