Caramelize the onions

Cup of Yum
1. Melt the butter in a large nonstick skillet over medium heat.
2. Add the thinly sliced onions, seasoning with the salt. This will help them cook down more quickly.
3. Stir the onions occasionally until they have begun to caramelize, about 15-20 minutes.
4. When the onions are a deep brown, add the red wine to deglaze the pan. (If you don't want to use wine, use the same amount of beef stock.)
5. Cook until all the wine has evaporated out of the onions, then remove from the heat to let cool.

Prepare the bread

1. While the onions cook down, slice the sourdough into 1″ squares. Keep in mind that we do not want to cut all the way through the bread.
2. Use a serrated knife to slice 1" slices on the diagonal into the bread, careful not to cut all the way through the bottom.
3. Spin the bread 90 degrees, and cut slices going this direction, forming the squares or diamonds.

Make the cheese sauce

1. Preheat the oven to 350°F. Place two pieces of aluminum foil on a baking sheet, shaping them into a plus sign. (These will wrap around the bread as it bakes.)
2. In the same pan that the onions were cooked in, add the shredded cheeses and milk.
3. Stir constantly, allowing the cheese a chance to melt.
4. Season with the thyme and black pepper. Remove from the heat.
5. Once the cheese sauce has finished cooking, pry open the bread pieces using your fingers or two butter knives and drizzle the cheese in. Top with the onions.
6. Complete this process until every nook and cranny of the bread has been filled with cheese and onion.
7. Wrap the bread in the prepared foil, and bake for 15-20 minutes.
8. Enjoy immediately!