Onion Tart

Ingredients

• 1 Egg yolk (Separate the white from the yolk)
• 155 g Butter (125 g for the dough, 30 g for cooking the onions, at room temperature for the dough)
• 250 g All-purpose flour (Sift before use)
• 1 pinch Salt
• 30 ml Cold water (To bind the dough)
• 1 kg Yellow onions (Peel and finely slice)
• 10 cl Milk
• 20 cl Water (For cooking the onions and the mixture)
• 3 tablespoons Thick crème fraîche
• 3 Eggs (Lightly beaten)
• 1 pinch Freshly ground pepper (Freshly ground)

Instructions

1. Prepare the shortcrust pastry

   In a bowl, mix the flour and the pinch of salt. Add the diced butter and work it with your fingertips until a sandy texture is achieved. Make a well in the centre, pour in the egg yolk diluted with 30 ml cold water, then quickly incorporate until a homogeneous dough forms.

   Time: PT10M

2. Shape and refrigerate the dough

   Form a ball, wrap it in cling film and place it in the refrigerator for 15 minutes to relax.

   Time: PT15M

3. Slice the onions

   Peel the onions then cut them into thin slices or small dice according to preference.

   Time: PT10M

4. Sauté the onions

   Melt 30 g butter in a pan over medium heat. Add the onions, lightly salt and cook while stirring regularly until they become translucent then lightly golden.

   Time: PT15M

5. Deglaze and soften the onions

   Pour 20 cl water into the pan, cover and let simmer for 5 minutes until the onions are tender and the liquid has almost evaporated.

   Time: PT5M

6. Prepare the cream mixture

   In a bowl, whisk the 3 eggs with the milk (10 cl), the remaining water (20 cl), the crème fraîche, salt and freshly ground pepper.

   Time: PT5M

7. Combine the onions and the mixture

   Incorporate the cooked onions (and their juice) into the egg mixture, mixing well.

   Time: PT5M

8. Line the tart pan

   On a lightly floured surface, roll out the dough to a 3 mm thick disc. Place it in the 20 cm pan, press the edges and prick the base with a fork.

   Time: PT5M

9. Pour the filling

   Pour the onion‑egg mixture evenly over the tart base.

   Time: PT3M

10. Bake

    Bake the tart in the preheated oven at 180°C for 40 minutes, until the surface is golden and the filling is set.

    Time: PT40M

    Temperature: 180°C

11. Rest and serve

    Remove the tart from the oven, let rest for 5 minutes before unmolding and serving.

    Time: PT5M

Nutrition Facts

Calories

470

Protein

12 g

Carbohydrates

45 g

Fat

30 g

Fiber

4 g

Ingredient Substitutions

• Instead of Egg yolk: 1 tablespoon water + 1 teaspoon vinegar (binder)
• Instead of Butter: Vegetable margarine (for the dough)
• Instead of All-purpose flour: Whole wheat flour (for a more rustic version)
• Instead of Yellow onions: Shallots (for a milder flavor)
• Instead of Milk: Almond milk (for a lactose‑free version)
• Instead of Thick crème fraîche: 20% liquid cream
• Instead of Eggs: Silken tofu (for a vegan version, but different texture)
• Instead of Freshly ground pepper: White pepper

Equipment Needed

• Work surface
• Chef's knife
• Cutting board
• Mixing bowl
• Oven
• 20 cm (diameter) by 5 cm deep tart pan
• Heavy‑bottomed skillet (saucepan)
• Wooden spoon
• Rolling pin
• Fork (for docking the dough)
• Whisk

Critical Steps — Do Not Skip

• Sablé the butter with the flour without overworking the dough.
• Cook the onions until golden but not burnt.
• Do not let the onions get too hot before mixing with the eggs.

Chef Tips from the Video

• Add a pinch of grated nutmeg to the mixture for a subtle aromatic note.
• Lightly sprinkle grated cheese (Gruyère or Comté) before baking for an even richer crust.
• Serve the tart warm with a vinaigrette green salad to balance the rich flavor.

Troubleshooting

Storage

Refrigerator: Store in an airtight container for 3 days.

Freezer: Not recommended, the pastry texture may deteriorate.

Room temperature: Consume within 2 hours after cooking.

Make-Ahead Tips

• The shortcrust pastry can be prepared the day before and kept in the refrigerator.
• Cooked onions can be prepared 24 hours ahead and gently reheated.