Turn the slow cooker to high. Add 4 cups of beef bone broth, bay leaves, and red pepper flakes.

Heat a large skillet over medium-high heat. Season the London broil with salt and pepper. Add 2 tablespoons of butter and 1 tablespoon of olive oil to the skillet. Once melted, sear the London broil on all sides until golden brown, about 2-3 minutes per side. Transfer the seared beef to the slow cooker and cover.

Reduce the heat to medium. Add the remaining butter to the skillet. Once melted, stir in the sliced onions and sugar. Cook for about 25 minutes, stirring occasionally, until the onions are soft and caramelized. In the last 8 minutes, add the minced garlic and cook until fragrant.

Pour the red wine into the skillet to deglaze, scraping up the brown bits from the bottom with a wooden spoon. Let the wine reduce for 1-2 minutes. Pour the onion mixture over the London broil in the slow cooker.

Add the cherry tomatoes and thyme into the broth around the beef.

Cover and cook on high for 3-4 hours or on low for 6-7 hours, until the London broil is tender.

About 10 minutes before serving, preheat your broiler. Arrange slices of bread on a baking sheet and toast under the broiler for 1-2 minutes on each side, or until golden and crisp. Then, top with cheese and continue broiling until the cheese is melted and bubbly.

Slice or shred the London broil and serve with the rich onion and tomato soup with 1-2 pieces of cheese bread on top.