Parboil the rotini pasta in boiling salted water for 8 minutes, and strain.
Heat the olive oil in a pan over medium heat, add the sliced onions and a pinch of sea salt to the pan and saute for 8 minutes. Reduce the heat to medium-low and saute for another 35 minutes, or until caramelized.
Render the sausage in a dry pan over medium heat for 10 minutes, until crispy bits form. Add milk, half-and- half, caramelized onions, sea salt, and ground pepper and bring to a boil. The second the mixture starts to boil, reduce the heat to medium-low, add the Cheddar cheese, Friulano cheese, and bay leaf and stir until the cheese is melted, about 5 minutes.
In a bowl, mix the cooked rotini pasta with the cheese sauce and transfer into a baking dish. Top with the panko bread crumbs, drizzle with melted butter and broil for a few minutes, or until the panko is golden brown and the edges crisp up.