1 tbsp. extra-virgin olive oil
1/2 yellow onion, finely chopped
2 stalks celery, finely chopped
leek, cleaned and thinly sliced (white and pale green parts only)
3 cloves garlic, minced
2 tsp. thyme, freshly chopped
1/2 tsp. red pepper flakes (optional)
Kosher salt
Freshly ground black pepper
4 c. low-sodium vegetable broth
2 c. water
2 (15.5-oz.) cans cannellini beans, drained and rinsed
Juice of 1 lemon
1 large bunch kale, removed from stems and torn into medium pieces
Freshly grated Parmesan, for serving