In a large skillet, heat 1 tbsp oil over medium-low heat. Add leeks, 3/4 tsp salt, and 1/4 tsp pepper. Cook, stirring often, until softened, about 10 minutes.
Add beans, broth and sage to pan; with a potato masher, mash about 1/3 of the beans. Bring to a boil; reduce to a simmer. Cook until sauce has thickened but is still soupy, about 10 minutes. Cool; transfer to a covered container and keep warm.
Meanwhile, in a large pot of boiling salted water, cook pasta according to package directions. Drain; rinse. Transfer to a bowl and toss with remaining tbsp of oil to coat.
In large 5-quart saucepan over medium heat, bring sauce and lemon juice to a simmer. Stir in cream and Parmesan. Add pasta; cook, stirring, until heated through. Serve sprinkled with more Parmesan cheese.