Step 1: Caramelize the Onions

• Preheat oven to 350°F (175°C).

• Heat 3 Tbsp. olive oil in a large skillet over medium heat.

• Add sliced onions, garlic, bay leaves, red pepper flakes, and thyme sprig.

• Season with 1½ tsp. Diamond Crystal salt (or 1 tsp. Morton kosher salt).

• Cook, stirring occasionally, for 15–20 minutes until the onions become golden and jammy.

Step 2: Prepare the Creamy Base

• In a large mixing bowl, combine cream cheese, mayonnaise, and sour cream.

• Stir well until smooth (a few lumps are okay).

Step 3: Mix the Dip

• Remove bay leaves and thyme sprig from the caramelized onions and discard them.

• Transfer the onions into the cream cheese mixture.

• Add 3 cups of Gruyère and season with freshly ground black pepper.

• Stir well until fully combined.

Step 4: Assemble the Dip

• Transfer the dip mixture into an 8-inch cast-iron skillet or a 2-quart ovenproof baking dish.

• Use a rubber spatula to spread it into an even layer.

Step 5: Make the Crispy Topping

• In a medium bowl, mix panko breadcrumbs, remaining 1 cup of Gruyère, 1½ tsp. olive oil, and remaining ¼ tsp. salt.

• Sprinkle the mixture evenly over the top of the dip.

Step 6: Bake the Dip

• Place in the preheated oven and bake for 25–30 minutes, until heated through and the top is lightly browned.

Step 7: Broil for a Golden Finish

• Turn on the broiler and broil for about 3 minutes, until the top is bubbling and golden brown.

• Let cool for 5 minutes before serving.

Step 8: Garnish and Serve

• Scatter fresh thyme over the top.

• Serve warm with baguette slices, pears, and red endive leaves for dipping.