CARAMELIZE: Heat the oil and butter in a large cast iron skillet over medium heat. Add the onions and let sauté for 5 minutes, stirring frequently. Add the thyme, sugar, and ¼ teaspoon kosher salt and continue to cook for a minimum of 25 and up to 45 minutes on medium-low heat. Stir the onions every 5 minutes so they caramelize evenly. If, at any point, the onions are caramelizing too fast, turn the heat down to low. When the onions are soft and golden, add the balsamic, and allow the onions to soak it in. Remove from heat.

TOSS IT IN: Spray the inside of your slow cooker with cooking spray to keep the dip from sticking. Add the onions and all the remaining ingredients except the brie and gruyère to the slow cooker.

SLOW COOK: Cover and cook for 2 hours on the high setting. Check and stir once or twice, if possible. Add diced brie cheese and stir to combine. Top with shredded Gruyère, cover, and continue cooking for another 20-25 minutes or until the Gruyère melts. Keep in mind, the cheese won’t form a brown crust in the slow cooker. It will melt and become stringy, though. See below for broiling instructions.

BUBBLY TOP: For a bubbly top, add the brie and cook in the slow cooker for 20 minutes. Then transfer the dip to a 2-quart baking dish sprayed with cooking spray. Top with Gruyère and let the cheese melt under the broiler for a few minutes. Serve warm with crostini slices or crackers.

OR OVEN: Complete step 1. Add all the ingredients except the gruyere to a bowl and stir to combine. Dump the ingredients out into a 2-quart baking dish. Top with the shredded gruyere and bake in an oven preheated to 375ºF for 45-50 minutes. Check the dip to ensure it’s not browning too much at any point. Broil for the last 45-60 seconds to get that golden crust on top!