Rinse and sort the dried red beans, removing any debris or broken beans.
Soak the beans using one of two methods: Overnight — place beans in a large bowl or pot, cover with water about 2 inches above the beans, and soak overnight; drain before cooking. Quick-soak — place beans in a 4.5‑quart (or larger) pot, cover with water about 2 inches above, bring to a boil, remove from heat, cover, and let sit 1 hour; then drain.
Heat a 4.5‑quart or larger Dutch oven or pot over medium-low and add 3 tablespoons of the olive oil. Add the diced onions and cook, stirring frequently, until tender, about 8–10 minutes.
Add the remaining 1 tablespoon olive oil, minced garlic, smoked paprika, cayenne, dried basil, rubbed sage, and fresh-ground black pepper. Cook, stirring, for about 1 minute until fragrant.
Add the diced green bell pepper and diced celery and cook, stirring occasionally, until softened, about 5 minutes.
Add the soaked and drained beans to the pot along with the bay leaf and 8 cups of water. Increase heat to high and bring to a boil.
Reduce heat to a simmer and cook uncovered until the beans are tender, about 45–60 minutes. Check doneness by tasting several beans for tenderness.
Turn off the heat. Remove one cup of beans to a bowl and mash them with a potato masher, then return the mashed beans to the pot and stir to thicken the sauce slightly.
Stir in the diced scallions, chopped parsley, and kosher salt. Start with 2 teaspoons salt, taste, and add more (up to 3 teaspoons) if needed.
Let the beans sit off the heat for 5–10 minutes before serving.
Cook the long-grain white rice according to package instructions and serve a scoop of beans over rice. Top with additional scallions, parsley, and a dollop of sour cream or vegan sour cream if desired.