Hello Arthur. Caramelizing onions traditionally takes anywhere from 45 to 60 minutes because you have to slowly evaporate the water content before the natural sugars can break down and undergo the Maillard reaction. Since you are in a rush for your family stew tonight, there are two reliable methods you can use to cut that time down to about 15 minutes.
The most effective shortcut is adding a tiny pinch of baking soda. Use roughly one-eighth of a teaspoon per pound of sliced onions. The baking soda increases the pH of the onions, which accelerates the chemical browning process and softens the cell walls much faster. Keep in mind that this makes the onions softer and slightly more jam-like, but for a rich stew, that texture melts into the broth perfectly. Just be careful not to use more than a pinch, or it could alter the flavor.
The second method is using higher heat combined with frequent water deglazing. Heat your skillet over medium-high heat with your oil or butter and add the onions. Stir frequently. As soon as a brown glaze begins to stick to the bottom of the pan, pour in one or two tablespoons of water, scrape up all the browned bits from the pan with a wooden spoon, and stir them back into the onions. Repeat this process every time the pan dries out and begins to brown again. This distributes the rich color and flavor throughout the onions quickly without letting them burn.
Using these two tips together will give you deep, flavorful onions in a fraction of the usual time. I hope your stew turns out delicious.