Step 1

Drain and rinse 2 cans white beans and set aside. Finely chop 1 medium yellow onion and mince 4 cloves garlic.

Step 2

Heat 2 tablespoons olive oil in a Dutch oven or large pot until shimmering. Add the onion and sauté until softened and translucent, 3 to 5 minutes. Add the garlic and 1/4 teaspoon red pepper flakes, if using, and sauté until fragrant, about 1 minute more.

Step 3

Pour in 4 cups low-sodium vegetable or chicken broth, 1 can diced tomatoes and their juices, and the white beans. Add 2 fresh rosemary sprigs, 1 teaspoon kosher salt, 1/4 teaspoon black pepper, and 1 Parmesan rind, if using, and stir to combine. Bring to a boil. Reduce the heat to maintain a simmer, and simmer uncovered for 10 minutes to allow the flavors to meld.

Step 4

Stir in 5 ounces baby spinach (about 5 packed cups), a few handfuls at a time, until just wilted, 1 to 2 minutes. Serve garnished with grated Parmesan cheese.