In a large skillet, heat the olive oil over medium-low heat.
Add the sliced onions, seasoning them with a pinch of salt. Cook gently, stirring occasionally, for about 15-20 minutes, or until the onions are soft and deeply caramelized. If they start to stick, you can add a splash of water to prevent burning.
Once the onions are caramelized, stir in the minced garlic and cook for an additional 1-2 minutes until fragrant.
Add the drained butter beans to the skillet and gently fold them into the onion mixture to combine.
Pour in the balsamic vinegar and sprinkle with dried thyme, salt, and pepper. Stir well and cook for another 5 minutes until everything is heated through.
Remove from heat and adjust seasoning if needed.
Serve warm, garnished with fresh chopped parsley.
Notes
Add a splash of water if onions start to stick while cooking.