In a skillet or braiser, gently sauté the minced onion in olive oil until soft and translucent.
Add the sausage meat, which you will have removed from its casings and broken up with a fork. Mix it with the onion and let it, too, sauté gently, breaking it up further, if need be, with a wooden spoon or spatula as it cooks.
When the sausage meat has lost its red color and is just beginning to brown around the edges, pour in a splash of white wine and let it evaporate.
Add the heavy cream or passata and simmer. If using heavy cream, let it simmer for just a minute or two, until the cream has reduced. If using passata, let it simmer until well reduced to sauce-y consistency and the oil separates.
While the sauce is simmering, bring a pot of water to a boil. Salt it well and add the gramigna. Cook until al dente.
When the pasta has cooked, transfer it to sauce, along with a small ladleful of the pasta water, and toss. Simmer until the sauce coats the pasta well.
Serve right away, with grated parmigiano-reggiano for those who want it.