Peel off the outer layer of 2 large sweet onions, cut them in half, then slice them thinly.
Heat 2 tablespoons salted butter in a large skillet over medium heat.
Add the onions and sauté for 5 minutes or until they start to soften.
Add 1 cup water, reduce the heat to medium-low, and cook for 50 to 60 minutes, stirring every few minutes. Cook until the onions are very soft, golden brown, and caramelized. Be patient, this takes time! Cooking time depends on the size of your onions and the temperature. Slow and low is best.
If the onions start to stick to the bottom of the pan, reduce the heat to low and add more water. Stir continuously to prevent burning.