Step 1

Preheat oven to 375°. Place a big pinch of saffron threads in a small bowl. Cut 1 lemon in half and squeeze juice of 1 half over saffron. Let sit 15 minutes. Meanwhile, slice remaining lemon half and remaining 1 lemon ¼" thick; remove any seeds. Set lemon slices aside.

Step 2

Using a chef’s knife, trim dark green tops and roots from 1 medium leek; discard. Slice white and green parts into ¾" rounds; place in a colander and rinse well to remove dirt (try to keep intact). Pat dry. Trim dark green tops and roots from 2–3 spring onions; discard. Slice onions in half lengthwise. Thinly slice 1–2 green garlic stalks or trim top quarter from 1 head of garlic to expose cloves.

Step 3

Heat ¼ cup extra-virgin olive oil in a large skillet over medium-high. Arrange leek in a single layer in skillet and cook, undisturbed, until starting to turn deep golden brown underneath, about 3 minutes. Using tongs, transfer leek to a plate, keeping rounds as intact as possible. Arrange spring onions, cut side down, in skillet (if using head of garlic instead of green garlic, add to skillet, cut side down, too). Cook, undisturbed, until dark golden brown, about 2 minutes. Transfer to plate with leek.

Step 4

Reduce heat to medium. Add green garlic and remaining ¾ cup extra-virgin olive oil to skillet and cook, stirring often, 30 seconds. Remove from heat and add saffron and lemon juice, reserved lemon slices, 2 bay leaves, and 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt. Drain one 12–15.5-oz. jar white beans (such as gigante, corona, cannellini, or navy) in a colander and rinse under cold running water. Add beans to skillet and gently stir to coat in flavored oil. Nestle leek and spring onions (and head of garlic, if using), browned side up, into beans.

Step 5

Cover skillet and bake in oven until alliums are starting to soften, about 20 minutes. Remove skillet from oven, uncover, and gently stir beans to ensure they are mostly submerged. Re-cover skillet and continue to bake until alliums are meltingly tender and lemons are soft and jammy, 15–20 minutes more. Uncover and let sit 5 minutes.

Step 6

Serve straight from skillet or transfer to a shallow bowl. Top with ¼ cup dill fronds and ¼ cup mint leaves and sprinkle generously with flaky sea salt. Serve with crusty bread for sopping up oil.