Ingredients (Serves 6)

For the caramelized onions

• 3 lbs onions (yellow or sweet), thinly sliced

• 3 tbsp butter

• 2 tbsp olive oil

• 1 tsp salt

• ½ tsp black pepper

• 1 tsp sugar (optional, helps caramelize)

• 2–3 tsp fresh thyme or 1 tsp dried

• 2 cloves garlic, minced (optional)

Casserole base

• 1 cup heavy cream or half-and-half

• ½ cup sour cream (optional for tang)

• 1 cup shredded Gruyère or Swiss cheese

• ½ cup Parmesan, grated

• 1 tbsp flour (for thickening)

• 1 tsp Dijon mustard (optional but excellent)

Topping

• 1 cup buttery breadcrumbs (panko preferred)

• 2 tbsp melted butter

• ¼ cup Parmesan

🧑‍🍳 Instructions

1. Caramelize the onions (most important step)

1. Heat butter and olive oil in a large skillet over medium heat.

2. Add onions, salt, pepper, and sugar (if using).

3. Cook 35–45 minutes, stirring occasionally, until deep golden brown.

   • Lower heat if they brown too fast.

4. Add garlic and thyme during the last 5 minutes.

5. Remove from heat.

2. Make the creamy mixture

1. In a bowl, whisk together cream, sour cream (if using), flour, and Dijon.

2. Stir in Gruyère and Parmesan.

3. Fold in the caramelized onions until everything is coated.

3. Assemble the casserole

1. Preheat oven to 375°F (190°C).

2. Grease a 9×9 or similar baking dish.

3. Spread the creamy onion mixture evenly in the dish.

4. Add topping

1. Mix breadcrumbs, melted butter, and Parmesan.

2. Sprinkle evenly over the top.

5. Bake

• Bake 20–25 minutes until bubbly and golden.

• Let it cool 5–10 minutes before serving.