Ingredients:

  • 2 lbs yellow onions, thinly sliced pole-to-pole
  • 2 tbsp unsalted butter
  • 1 tbsp extra virgin olive oil
  • 0.5 tsp kosher salt
  • 2 tbsp dry sherry
  • 8 oz full-fat cream cheese, softened
  • 0.5 cup full-fat sour cream
  • 0.25 cup mayonnaise
  • 2 cloves garlic, minced
  • 1 tsp fresh thyme leaves, chopped
  • 0.5 tsp freshly ground black pepper
  • 6 oz Gruyère cheese, freshly shredded
  • 2 oz Parmesan cheese, freshly grated

Instructions:

  1. Melt butter and olive oil in a large heavy-bottomed skillet over medium heat until the butter stops foaming. Add sliced onions and salt.
  2. Cook onions for 35 to 45 minutes, stirring every 5 minutes until onions are deep mahogany and jammy. Reduce heat to medium low.
  3. Deglaze the pan by adding the dry sherry, scraping the bottom until all the brown bits are incorporated and the liquid has evaporated. Remove from heat to cool slightly.
  4. In a medium bowl, combine 8 oz softened cream cheese, 0.5 cup sour cream, 0.25 cup mayo, 2 cloves minced garlic, 1 tsp thyme, and 0.5 tsp pepper. Stir until the mixture is silky and uniform.
  5. Stir in 4 oz of the shredded Gruyère (save 2 oz for the top) and the 2 oz of Parmesan.
  6. Spread the mixture into your baking dish and sprinkle the remaining 2 oz of Gruyère over the top.
  7. Bake at 375°F for 20 to 25 minutes until the top is golden brown and the edges are bubbling.