Description
Delicious caramelized onion and Gruyere tartlets made with flaky puff pastry and a creamy filling.
Ingredients
Scale
- 1 sheet (about 9.5” x 10.5″ / 24 x 27 cm) all-butter puff pastry, thawed but still cold
- 4 cups (650 g) yellow onions, peeled and sliced 1/4″ (6 mm) thick
- 1 tbsp (8 g) olive oil
- 2 tbsp (28.5 g) unsalted butter
- 1 tsp (6 g) salt
- 1/4 tsp (1 g) ground nutmeg
- 1/4 tsp (1 g) freshly cracked black pepper, coarse grind
- 2 egg yolks
- 1/2 cup (120 g) whipping cream
- 1 cup (100 g) grated Gruyere cheese
- 2 tbsp grated Gruyere cheese (for topping)
- 1 tbsp (15 g) Dijon mustard
Instructions
- Step 1: Roll out the puff pastry sheet to fit a removable bottom tart pan with a rim 3/4″ to 1″ (2–2.5 cm) high. Place the rolled pastry in the tart pan, forming the rim. Chill in the refrigerator to keep the pastry cold and help maintain flakiness.
- Step 2: Peel and slice yellow onions uniformly to about 1/4-inch (6 mm) thickness using a sharp knife, mandolin slicer, or food processor. Uniform slices ensure even caramelization.
- Step 3: Heat butter and olive oil in a large sauté pan over medium heat. Add sliced onions, salt, freshly cracked black pepper, and ground nutmeg. Stir occasionally to prevent sticking and burning, flipping or mixing every 5 minutes. Adjust heat to medium-low if onions brown too quickly. Continue cooking until onions turn golden and caramelized, about 25-30 minutes.
- Step 4: Remove the cooked onions from heat and allow them to cool for about 10 minutes to prevent the eggs from cooking when combined.
- Step 5: In a bowl, whisk together 2 egg yolks and 1/2 cup (120 g) whipping cream until smooth. Stir the cooled caramelized onions into this mixture.
- Step 6: Take the chilled tart shell out of the refrigerator. Spread 1 tbsp (15 g) Dijon mustard evenly on the bottom of the pastry using the back of a spoon.
- Step 7: Spoon the onion and egg mixture evenly over the mustard-lined pastry shell. Smooth the surface gently with a spatula.
- Step 8: Sprinkle 2 tbsp grated Gruyere cheese evenly over the filling.
- Step 9: Preheat the oven to 375°F (190°C). Place the tart on the bottom rack of the oven. Bake for approximately 40 minutes or until the tart is golden brown, bubbly, and has a slightly puffed crust. Check for an aromatic smell and visual golden color as indicators of doneness.
- Step 10: Remove the tart from the oven and cool on a wire rack for a few minutes to set the filling. This also makes slicing easier.
Notes
- Store the tart in an airtight container at room temperature and consume within 2 days to preserve freshness and texture.
- Place in an airtight container in the refrigerator. Keep up to 5 days for flavor development and to prevent spoilage.
- Wrap tightly in plastic wrap, then place in a freezer-safe container. Freeze for up to 2 months. Thaw in the refrigerator overnight before reheating.
- Use yellow onions for their natural sweetness and even caramelization.
- Keep puff pastry cold to maintain flakiness; chilling after fitting it into the tart pan helps prevent shrinking and sogginess.
- Stir onions every 5 minutes during cooking for even color and flavor development. Lower heat if onions brown too fast.
- Cool caramelized onions 10 minutes before mixing with eggs and cream to avoid curdling the mixture.
- If pastry tears, patch gently with small piece of dough and brush with beaten egg to seal.
- To prevent sogginess in crust, sprinkle 1 tbsp cornmeal on pastry bottom before adding filling.
Nutrition
- Serving Size: 1 tartlet
- Calories: not explicitly stated
- Sugar: not explicitly stated
- Sodium: not explicitly stated
- Fat: not explicitly stated
- Saturated Fat: not explicitly stated
- Unsaturated Fat: not explicitly stated
- Trans Fat: not explicitly stated
- Carbohydrates: not explicitly stated
- Fiber: not explicitly stated
- Protein: not explicitly stated
- Cholesterol: not explicitly stated