Traditional Onion Tart

Ingredients

• 200 g All-purpose flour (Sift before use)
• 100 g Cold butter (Cut into small cubes, very cold)
• 1 pinch Fleur de sel (Adjust to taste)
• 50 ml Very cold water (Add gradually until a ball forms)
• 1 teaspoon Herbes de Provence (Optional, to flavor the dough)
• 500 g Pink onions (or white) (Peeled and sliced into strips)
• 2 tablespoons Olive oil (For cooking the onions)
• 1 tablespoon Whole grain mustard (Spread on the bottom of the tin)
• 200 ml Heavy cream (Can be replaced with whipping cream)
• 1 Egg (Beaten)
• to taste Salt & pepper (Season the filling)

Instructions

1. Prepare the dough

   In a large bowl, combine the flour, Herbes de Provence and fleur de sel. Add the cold butter in pieces and work it with your fingertips until a sandy texture forms with small butter specks.

   Time: PT15M

2. Shape and rest the dough

   Gradually pour the cold water while mixing until a dough ball forms. Shape into a disc, wrap in cling film and refrigerate for 30 minutes.

   Time: PT30M

3. Caramelize the onions

   Peel the onions and slice into strips. Heat olive oil in a pan over medium heat, add the onions and sauté for 15‑20 minutes, stirring regularly until they are soft and lightly golden.

   Time: PT20M

4. Roll out the dough and place in the tin

   On a lightly floured surface, roll out the dough to a 3 mm thick circle. Lay it into the tart tin, gently press the edges and trim excess. Prick the base with a fork.

   Time: PT10M

5. Prepare the filling

   Spread the whole grain mustard on the dough base. Distribute the caramelized onions evenly. In a bowl, whisk the heavy cream with the egg, add a pinch of fleur de sel, pepper and mix.

   Time: PT5M

6. Pour the custard

   Gently pour the cream‑egg mixture over the onions, ensuring the entire surface is covered.

   Time: PT2M

7. Bake

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

   Time: PT40M

   Temperature: 180°C

8. Rest and serve

   Remove the tart from the oven, let it rest 5‑10 minutes before slicing. Serve warm with a green salad.

   Time: PT10M

Nutrition Facts

Calories

350

Protein

8 g

Carbohydrates

30 g

Fat

22 g

Fiber

3 g

Ingredient Substitutions

• Instead of All-purpose flour: whole wheat flour
• Instead of Cold butter: unsalted margarine
• Instead of Fleur de sel: table salt
• Instead of Very cold water: ice water
• Instead of Herbes de Provence: dried thyme
• Instead of Pink onions (or white): yellow onions
• Instead of Olive oil: sunflower oil
• Instead of Whole grain mustard: Dijon mustard
• Instead of Heavy cream: whole milk + butter
• Instead of Egg: 1/4 cup applesauce (vegan)
• Instead of Salt & pepper: sea salt, black pepper

Equipment Needed

• Large bowl
• Rolling pin
• Cling film
• Frying pan
• Wooden spatula
• High‑edge tart tin
• Oven
• Whisk
• Chef's knife
• Cutting board

Critical Steps — Do Not Skip

• Use very cold butter and work it with fingertips to obtain specks.
• Do not overwork the dough to avoid excessive gluten development.
• Caramelize the onions until golden without burning.
• Bake the tart until well golden to ensure a crispy crust.

Chef Tips from the Video

• Sprinkle a little grated cheese (Gruyère) on top before baking for extra richness.
• Use a preheated oven for an even temperature rise.
• Let the tart rest 5 minutes after removing from the oven to facilitate slicing.

Troubleshooting

Storage

Refrigerator: Store in an airtight container, covered with cling film. Keeps up to 3 days.

Freezer: Wrap the cooled tart in cling film then aluminum foil. Can be kept for 1 month. Thaw in the refrigerator before reheating.

Room temperature: Consume the same day, otherwise refrigerate.

Make-Ahead Tips

• Prepare the dough the day before and keep it refrigerated.
• Caramelize the onions ahead of time, reheat slightly before assembling.
• The cream mixture can be prepared 2 hours ahead and kept chilled.