
Heat a large skillet over medium heat. Put the bacon in the skillet and cook until it is crisp. Using a slotted spoon, remove the bacon from the pan and set aside; leaving half of the drippings in the pan.
Reduce the heat to medium-low. To the bacon drippings, add the butter, onion, thyme, black pepper, and cayenne. Cook until the onions are caramelized, 25 to 30 minutes. Mix the cooked bacon in with the caramelized onions.
Add the sherry and brown sugar erythritol. Mix in and cook for an additional 5 to 10 minutes, until the sherry has evaporated and the erythritol has had time to caramelize. Store the jam in the refrigerator for up to 1 week.