Caramelized Onion Gruyere Tart

Imagine the aroma of slow-cooked onions filling your kitchen as they transform into a sweet, golden marmalade. This Caramelized Onion and Gruyere Tart is the epitome of sophisticated comfort food, combining the earthy sweetness of yellow onions with the nutty, melting qualities of aged Gruyere cheese. Wrapped in a buttery, flaky puff pastry, this dish is a celebration of simple, high-quality ingredients working in perfect harmony.

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Whether you are hosting a weekend gathering or looking for a special weekday treat, this tart brings a touch of French bistro charm to your home. The rich custard filling, lightened by whole milk and heavy cream, provides a silky backdrop for the intense flavor of the onions and the sharp bite of the Gruyere.

Ingredients

Pastry

• 1 9-inch (23 cm) round sheet of puff pastry, thawed if frozen

Caramelized Onions

• 2 tablespoons unsalted butter
• 2 tablespoons olive oil
• 4 large yellow onions, thinly sliced
• 1 teaspoon salt
• 1/2 teaspoon freshly ground black pepper
• 1 teaspoon sugar
• 2 teaspoons fresh thyme leaves (or 1 teaspoon dried thyme)

Filling

• 3 large eggs
• 1 cup (240 ml) heavy cream
• 1/2 cup (120 ml) whole milk
• 1/4 teaspoon ground nutmeg
• 1/2 teaspoon salt
• 1/4 teaspoon freshly ground black pepper
• 1 1/2 cups (150 g) Gruyere cheese, grated
• 1 tablespoon Dijon mustard

Instructions

Step 1

Preheat the oven to 375°F (190°C).

Step 2

Roll out the puff pastry and fit it into a 9-inch (23 cm) tart pan with a removable bottom. Trim any excess. Prick the base with a fork. Chill in the refrigerator while preparing the filling.

Step 3

In a large skillet over medium-low heat, melt butter with olive oil. Add onions, salt, pepper, and sugar. Cook, stirring frequently, until onions are golden brown and caramelized, about 30–35 minutes. Stir in thyme during the last 5 minutes. Remove from heat and let cool slightly.

Step 4

In a mixing bowl, whisk together eggs, heavy cream, milk, nutmeg, salt, and pepper until smooth.

Step 5

Brush the base of the chilled pastry shell with Dijon mustard. Spread the caramelized onions evenly over the base. Sprinkle with grated Gruyere cheese.

Step 6

Pour the egg mixture evenly over the onions and cheese.

Step 7

Bake for 35–40 minutes, until the filling is set and the top is golden brown.

Step 8

Let cool for 10 minutes before slicing and serving.

Zusatztipps für die Zubereitung

For added depth and a touch of acidity, add a splash of white wine to the onions during the final stages of caramelization. Ensure the onions are cooked over a gentle heat to prevent burning, as this ensures the most delicate sweetness.

Varianten und Anpassungen

While Gruyere is traditional for its nutty profile, you can easily substitute it with Emmental or Swiss cheese if preferred. For a different herb profile, rosemary or savory can be used in place of thyme.

Prep meals effortlessly by chopping vegetables, slicing meats, and serving dinner with the right knife always ready.

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Serviervorschläge

To complete this elegant meal, serve the tart alongside a fresh bed of mixed greens dressed in a light vinaigrette. Pair it with a crisp white wine, such as a Sauvignon Blanc, to cut through the richness of the cheese and cream.

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This tart contains milk, eggs, and wheat (gluten); always check your labels for potential contamination if allergies are a concern. With 410 calories and 13g of protein per serving, it offers a satisfying and nutritious main dish for any vegetarian gathering.

Recipe Guide

→ How long should I caramelize the onions?

Cook thinly sliced onions in butter and olive oil over medium-low heat for about 30–35 minutes, stirring frequently until they turn golden brown and sweet.

→ Can I substitute Gruyere cheese with another type?

Yes, Emmental or Swiss cheese can be used as suitable alternatives to Gruyere for a similar melting texture and flavor.

→ What pastry works best for this tart?

Using a 9-inch sheet of puff pastry creates a flaky and buttery base that complements the savory filling perfectly.

→ Is it necessary to chill the pastry before filling?

Yes, chilling the pastry after fitting it in the pan helps prevent shrinking and maintains its shape during baking.

→ How can I enhance the flavor of the caramelized onions?

Add a splash of white wine while cooking the onions to deepen their sweetness and complexity.