Heat olive oil in an oven-safe skillet over medium heat. Add sliced onions and cook until softened and starting to turn translucent.
Stir in garlic, thyme, oregano, parsley, and red pepper flakes. Cook for about 30–60 seconds until everything is combined and fragrant.
Pour in the crushed tomatoes and salt. Stir and let the sauce simmer for about 5 minutes until slightly thickened.
Add the butter beans and stir to coat. Reduce heat and let simmer for 10–15 minutes so the beans absorb the sauce.
Preheat the oven to 400°F. Remove the pan from heat and sprinkle mozzarella and parmesan evenly over the top.
Bake for 12–15 minutes until the cheese is melted and lightly browned. For extra browning, broil for a few minutes at the end.
Remove from the oven, garnish with fresh basil, and serve warm with toasted bread or over polenta.
Notes
• Use canned beans for convenience: Two cans of butter beans work well here. Just drain and rinse before adding.• Marinara shortcut: You can replace the crushed tomatoes and spices with about 3½ cups of marinara sauce to save time.• Cheese coverage tip: Spread the mozzarella and parmesan evenly so you get a consistent melted layer across the top.• For extra browning: Broil for the last 2–3 minutes if you want a more golden top. Keep an eye on it so it doesn’t burn.• Make it heartier: Add chickpeas or another white bean along with the butter beans for a slightly more filling version.• Storage tip: Store leftovers in the fridge for up to 4 days and reheat until warmed through.