Ruth’s Chris Caramelized Onion & Gruyère Tart – Elegant Appetizer

Instructions:

1. Preheat the oven to 400°F (205°C). Line a baking sheet or tart pan with parchment paper.
2. Heat the butter and olive oil in a skillet over medium-low heat.
3. Add the sliced onions and salt. Cook slowly, stirring occasionally, for 25–30 minutes until deeply caramelized and golden.
4. Stir in the black pepper and thyme, then remove from heat and allow the onions to cool slightly.
5. Roll the puff pastry onto the prepared pan. Score a 1-inch border around the edges, being careful not to cut all the way through.
6. Lightly prick the center of the pastry with a fork to prevent excessive puffing.
7. In a small bowl, whisk together the heavy cream, egg, and Dijon mustard.
8. Spread the caramelized onions evenly over the center of the pastry.
9. Sprinkle the Gruyère cheese evenly over the onions, then drizzle the cream mixture over the top.
10. Bake for 18–22 minutes, until the pastry is puffed and golden and the filling is set and bubbly.
11. Let cool slightly, garnish if desired, slice, and serve warm or at room temperature.

Variations

• Add crispy bacon or pancetta for a richer, smoky flavor.
• Substitute fontina or Comté for Gruyère for a slightly different nutty profile.
• Add sautéed mushrooms for an earthier tart.
• Use shallots instead of onions for a milder, sweeter taste.

Tips

• Cook the onions slowly and patiently; rushing this step will sacrifice flavor.
• Freshly grated cheese melts more smoothly than pre-shredded.
• Brushing the pastry edges with melted butter after baking adds shine and richness.
• This tart can be baked ahead and gently reheated just before serving.