Melt 2 tablespoons of butter and 1 tablespoon of olive oil over medium heat in a large skillet. Add the sliced onions and cook for about 25–30 minutes until they caramelize.

Slice the Yukon Gold potatoes into ¼-inch thick rounds and pat them dry with paper towels.

In a mixing bowl, whisk together the beef broth, heavy cream, Worcestershire sauce, and fresh thyme. Season with salt and black pepper.

Preheat your oven to 350°F (175°C). In a greased baking dish, layer the potatoes, caramelized onions, and the cheese mixture. Drizzle the liquid mixture over the layers.

Cover with aluminum foil and bake for 45 minutes. Then remove the foil and bake for an additional 20–30 minutes until the top is golden and bubbly.

Let the dish rest for 10 minutes before serving.