½ cup extra-virgin olive oil
1 large white onion, halved and thinly sliced into half moons
Fine sea salt
6 garlic cloves, thinly sliced
2 teaspoons minced fresh rosemary, or ½ teaspoon dried rosemary
¼ teaspoon red-pepper flakes, more for serving
2 (15-ounce) cans white beans, such as cannellini or butter beans (preferably canned with salt), drained and rinsed
1 cup chopped tomatoes, fresh or canned
1½ teaspoons finely grated lemon zest
1 cup chopped fresh parsley leaves and tender stems, more for garnish

In a large skillet, heat 2 tablespoons oil until it shimmers over medium-high heat. Add onion and cook, stirring occasionally, until well browned all over, 7 to 10 minutes. Reduce heat to medium, transfer half of the onions to a plate and season lightly with salt.

Add remaining 6 tablespoons oil, the garlic, rosemary, red-pepper flakes and a pinch of salt to the onions in the skillet. Cook until garlic is pale gold at the edges (don’t let the garlic turn brown), 2 to 5 minutes.

Add beans, chopped tomatoes, ½ cup of water and 1 teaspoon salt to skillet; stir until beans are well coated with sauce. Bring to a simmer over medium-low heat and cook until broth thickens, stirring occasionally, about 10 to 15 minutes.

Stir in lemon zest and parsley, and taste, adding more salt if needed. Garnish with reserved onions, more parsley, olive oil and red-pepper flakes, if you’d like. The beans thicken as they cool, but you can add more water to make them brothier if you like.

By Melissa Clark