To the bowl of your crockpot, add the butter, onions, garlic, brown sugar and worcestershire sauce. Stir everything together, cover the crockpot and cook on low for at least 8 hours or up to 14 hours. I like cooking the onions overnight while I sleep (note that I have noticed that all crockpots cook differently, if yours seems to cook fast, check the onions at 8 hours in to make sure nothing is burning).
The next morning, stir the flour into the onions and then add the beer (or wine), beef broth, bay leaves, thyme and a good pinch of pepper. Cover and cook on low for 6-8 hours or on high for 3-4 hours. The longer and slower you can cook this the better. Taste and season with salt + pepper if needed.
Just before you're ready to eat, make the french toast. In a shallow bowl, whisk together the eggs, milk, parmesan and a pinch of salt + pepper.
Preheat the broiler to high.
Heat a large skillet over medium heat and add the butter to melt.
Submerge one piece of toast at a time into the egg mixture, allowing it to sit 30 seconds in the eggs. Remove and allow the excess to drip off back into the bowl. Place the toast on the hot skillet and cook until golden brown, about 3 minutes per side. Repeat with the remaining bread.
Ladle the french onion soup into oven safe ramekins or bowls. Place 1-2 pieces of toast on top of the soup and cover with cheese. Place the ramekins on a baking sheet and place under the broiler for 30 seconds to 1 minute, or until the cheese is melted. WATCH close, the broiler works quick!
Serve the soup with fresh thyme and enjoy hot, right out of the oven!