French Onion Soup Deviled Eggs

Hard Boil the Eggs: Place the eggs in a large saucepan and cover with cold water. Bring to a boil over medium-high heat. Once boiling, remove from heat, cover, and let sit for 10 minutes. Drain the hot water and immediately rinse with cold water to stop the cooking process. Peel the eggs and slice them in half lengthwise.

Caramelize the Onions: In a medium skillet, melt the butter and olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, until softened and deeply caramelized, about 20-25 minutes. Stir in the brown sugar and Worcestershire sauce (if using) during the last few minutes of cooking. Remove from heat and let cool slightly.

Prepare the Filling: Carefully scoop out the egg yolks into a mixing bowl. Add the mayonnaise, Dijon mustard, salt, and pepper to the yolks. Mash the yolks with a fork until smooth.

Combine the Filling: Add about half of the caramelized onions to the yolk mixture (reserve the rest for topping). Mix well to combine all the ingredients. Taste and adjust seasoning as needed.

Fill the Eggs: Spoon or pipe the yolk mixture into the hollowed-out egg whites. A piping bag will give a cleaner, more professional look.

Garnish and Serve: Top each deviled egg with a small amount of the reserved caramelized onions and a sprinkle of grated Gruyere cheese. Garnish with chopped fresh parsley, if desired. Serve immediately or chill for later.