Preheat your oven to 375°F (190°C). This helps ensure your casserole bakes evenly and gets that lovely bubbly, golden cheese topping.

In a large skillet, heat the olive oil over medium heat. Add the sliced onions and a pinch of salt. Cook slowly, stirring frequently, until the onions are deeply caramelized—about 25-30 minutes. My grandma always said patience is key, and I’ve found that slow caramelization makes all the difference in flavor.

While the onions cook, season the beef pieces with salt, pepper, and thyme. In another skillet or large pot, brown the beef over medium-high heat until nicely seared on all sides—about 5-7 minutes. This step adds a depth of flavor that’s worth the extra few minutes.

Add the minced garlic to the beef and cook for another minute until fragrant. Then, pour in the beef broth, red wine (if using), Worcestershire sauce, and Dijon mustard. Stir to combine, scraping up any browned bits from the bottom of the pan. Let the mixture simmer for about 10 minutes to meld the flavors.

Once the onions are caramelized and the beef mixture is ready, combine everything in a baking dish—preferably one that’s oven-safe and roomy enough to hold all those flavors. Spread the caramelized onions evenly over the beef mixture.

Sprinkle the shredded cheese generously over the top. I like to layer a little cheese in the middle and on top—this creates a gooey, cheesy layer that my family loves. Dot with small bits of butter for extra richness.

Place the casserole in the preheated oven and bake for 20-25 minutes, or until the cheese is melted, bubbly, and golden brown. Keep an eye on it during the last few minutes so the cheese doesn’t burn.

Once out of the oven, let it rest for about 5 minutes. This helps the flavors settle and makes serving easier. Garnish with chopped parsley for freshness and a pop of color.

Serve hot, with crusty bread or over mashed potatoes—whatever your heart desires. I often serve it with a simple green salad to balance the richness.