01 -
Slice off the top 1/4 of each onion and remove the root. Peel off any skin-like layers. Cut a star-shaped slit into the top without slicing through the outer two layers. Use a spoon to scoop out the inside, leaving two outer layers intact.
02 -
Chop the scooped-out onion insides and any remaining onions into a large dice.
03 -
Preheat a large pan over high heat and melt the butter. Add the diced onions, season with salt and pepper, and cook for 45 minutes, stirring occasionally, until deep brown and reduced to about 1 cup.
04 -
Stir in garlic, thyme, and additional butter. Cook for 2 minutes, then sprinkle in the flour and combine thoroughly.
05 -
Add the beef broth, stir, and bring to a simmer. Cook for 5 minutes until the mixture thickens. Adjust seasoning as necessary and remove from heat.
06 -
Preheat the oven to 425°F. Fill each hollowed onion with the caramelized mixture and place them in a baking dish. Bake for 30 minutes.
07 -
Cut sourdough slices into cubes and place them on a baking sheet. Bake for 15 minutes until crisp.
08 -
Top the baked onions with a layer of cheese, followed by croutons, then another layer of cheese. Broil on high for 5 minutes until the cheese melts and chars slightly.
09 -
Let the onions cool for 5 minutes before serving. Optionally pair with rice or a side dish of your choice.