In a large skillet, heat olive oil and butter over medium heat. Sauté chopped leeks for 4-5 minutes until golden and softened. Transfer to a plate and set aside.

In the same skillet, add onion and sauté for 3-4 minutes until translucent. Then, add minced garlic and cook for an additional minute.

Stir in cannellini beans with liquid and simmer gently for about 5 minutes.

Reduce heat to low and mix in miso paste, lemon juice, and rosemary. Stir thoroughly.

Cook pasta al dente, reserving 1/4 cup pasta water. Drain and add pasta to skillet with reserved water. Toss together.

Reintroduce sautéed leeks to the mixture and simmer on low for 1 minute. Adjust with more pasta water if needed.

Serve hot, topped with fresh lemon zest, grated parmesan, and cracked black pepper.