Unless using lima beans, soak the beans in a large bowl of water for at least 4 hours or overnight.
Drain the beans well. 2.
Transfer the drained beans to a large, heavy pot or Dutch oven.
Add the halved onion, the single crushed garlic clove, the bouquet garni, and 7 cups (1680 ml) of water.
Bring to a gentle boil, then reduce the heat to low, cover, and simmer for 1 hour.
Once done, remove and discard the onion and crushed garlic. 3.
While the beans simmer, heat the olive oil in a large skillet over medium heat.
Add the chopped leeks and a generous pinch of salt.
Cook, stirring occasionally, for about 5 minutes until the leeks have softened but not browned.
Stir in the minced garlic and cook for another 30 seconds until fragrant. 4. Carefully stir the cooked leeks and garlic into the pot with the beans.
Add the diced winter squash and bring the stew back to a simmer. If the aren't fully submerged, add another ½ to 1 cup (240 ml) of water.
Season generously with salt (about 2 teaspoons / 10 ml / 0.3 fl oz to start), cover the pot, and let it simmer for 30 to 60 minutes, until the beans are perfectly tender and the squash is soft enough to begin falling apart. 5.
Stir in the slivered fresh sage and season with black pepper.
Taste and adjust the salt if needed.
Remove and discard the bouquet garni before serving. Ladle the hot stew into bowls and garnish with a sprinkle of freshly grated Parmesan or Pecorino cheese, if desired.
Keep It Vegan: To make this recipe fully vegan, simply omit the Parmesan rind from the bouquet garni and skip the cheese garnish. For a cheesy flavor, sprinkle with nutritional yeast before serving.