Melt 2 tablespoons of unsalted butter with 1 tablespoon of olive oil over medium-low heat in a large skillet. Add 3 sliced yellow onions and a pinch of salt, stirring well. Cook for 30–40 minutes until deeply golden and caramelized.

Stir in 2 minced garlic cloves and 1 tablespoon of fresh thyme for the last minute of cooking. Optionally, drizzle in 1 tablespoon of balsamic vinegar, scraping the bottom of the pan.

Stir in 1 ½ cups of dry orzo and 4 cups of beef broth, bringing it to a simmer. Cook for 8–10 minutes until the orzo is nearly tender but still slightly firm.

Lower the heat to a simmer and incorporate 1 cup of heavy cream into the orzo mixture. Stir in half of the Gruyère and mozzarella cheese until melted.

Preheat your oven to 400°F (200°C). Transfer the orzo mixture to a greased baking dish, topping with the remaining cheese. Bake for 10–15 minutes until bubbly and golden brown.

Remove from the oven and let cool slightly. Garnish with parsley or chives before serving warm.