Pour 1-2 Tbsp of EVOO in your crockpot, add the sliced onions and sprinkle with salt and pepper.
Let cook on low for 4-5 hours, or high for 3-4. You want them to caramelize down and start to brown. Stir occasionally (or don’t, I’m a blogger not a cop!)
Add homemade beef or veggie broth enough to cover and then some (4-5 cups)
Add the red wine or dry cooking sherry (but really use wine, because who doesn’t need an excuse to open a bottle of wine? 😉 ). Let cook in the crockpot another couple of hours until the flavors have really blended. (The longer the better)
Fill sterilized canning jars with soup, leaving one inch of headspace.
Attach your lids and rings.
Process in a pressure canner:
60 minutes for pints
75 minutes for quarts