Melt 1 tablespoon butter in a small skillet over medium heat. Add the thinly sliced whites and greens of 3-4 scallions and cook until the scallions are soft and just starting to brown.
Add 1 cup cooked white beans with their broth to the skillet. Add more bean broth or vegetable broth if needed so the broth resembles a thin soup; I usually add 1/4 to 1/2 cup more liquid when the bean broth is on the thicker side.
Bring the mixture to a boil, then reduce the heat to a simmer and cook until the liquid has thickened and reduced slightly; it will still be somewhat brothy.
Remove the skillet from the heat and stir in 2 teaspoons light miso and 1-2 teaspoons lemon juice. Taste and adjust the seasoning, and finish with a solid amount of freshly cracked black pepper.
This dish makes a good-size serving for one person but can potentially serve two if paired with other items.