Put 2 T butter and 1 T olive oil in a 12-inch skillet and heat over medium-low heat. Put the onions in the skillet and stir them around to evenly coat with the butter/oil mixture. Keep the heat low and cook the onions for a solid 40 - 50 minutes. Set a timer. The onions will reduce in volume considerably. Around the 20 minute mark, they start getting a yummy brown color. Be patient. Stir occasionally. Once the onions are cooked, deglaze the pan with a little water, wine, or stock. Get all the brown bits off the bottom of the pan. Transfer the onions and deglazing liquid to a medium bowl.