Melt the butter in a pan. Sweat the chopped onion and chilies with a bit of salt and pepper until softened.
Turn up the heat. Add the spinach to the pan. Sprinkle with more salt and pepper. Cook, uncovered, over high heat, turning the spinach over often, until the mixture is almost dry.
Pour in the balsamic vinegar and honey. Continue cooking for another minute.
Taste and add more salt and pepper, as needed.