If using fresh beans, simmer them covered on low heat in enough water to cover by about 2 inches until tender, about 1 hour or less.
In a saute pan, cook pancetta and onion in 1 Tbsp olive oil over medium-high heat until the onion turns translucent. Add garlic, sage, and rosemary and cook about 1 minute, then reduce heat to minimum.
Drain beans, saving the cooking liquid. Add beans to the pan and mash about three-fourths with a wooden spoon. Stir in about 1/2 cup bean liquid to loosen. Season with salt and pepper.
Drain pasta as soon as it is cooked and toss immediately with the skillet contents. Add the remaining 2 Tbsp olive oil, sprinkle with Parmesan, toss once more, and serve. If the sauce feels too dense, thin with a little more bean liquid.
