A crisp buttery crust, melty caramelized onions and a savory custard makes the Alsatian Onion Tart a staple of French cooking. This rustic tart tastes rich, satisfying and brings a unique combination of sweet and salty flavors, with the sweet caramelized onions bound by a cheese and egg filling.

My version of an Alsatian Onion Tart

The Alsatian Onion Tart is lesser known than the Quiche Lorraine – hailing from the same French region – but is no less delicious.

As with most regional recipes, there isn’t just one recipe for Alsatian Onion Tart. Lots of variations of this recipe exist, but they almost always include three main components: a crisp and buttery pie crust, loads of caramelized onions and a savory custard poured over top, made of eggs and cream.

For caramelizing the onions, I like to use butter and beef stock, which both provide richness and classic earthy flavors. Some other recipes call for white wine instead of stock, which also works great as a slightly more expensive alternative.

Some variations, like in my recipe, include hard mountain cheese such as Gruyère or Emmental. Adding this cheese into the savory filling of this tart brings an added richness as well as a salty kick, which contrasts well against the sweet caramelized onions.

I also like to sprinkle caraway over the quiche just before baking. Caraway, known in French as “carvi”, is popular in Alsatian cuisine. It is often used to flavor dishes and commonly found in Munster, a flagship cheese of Alsace. This sprinkle of caraway is optional, but I think it brings out the true Alsatian flavors of this tart.  

Make your own crust, if you have time.  

Although you can use a store-bought pie crust for convenience, making your pie crust from scratch will go a long way. The recipe below only requires about 15 minutes of time. It guarantees a flaky, buttery crust that is the perfect vessel for the creamy custard. 

This recipe will make enough for a 9-inch (22.9cm) pie crust, plus a little extra if you want to make an individual tart on the side – or keep it in the freezer for another project (well-wrapped in plastic film). You definitely won’t regret taking the time and minimal extra effort to make it. 

The Caramelized onions

The caramelized onions are the stars of this recipe, so make sure they are done properly. Caramelizing onions, by slowly cooking them in butter and deglazing in stock until they are golden and melty, extracts the natural sugars from the onions and intensifies their flavor.  

For this recipe, the onions do not need to be caramelized too much. Reach for a golden color, not brown. The process of caramelizing onions should take about 30 minutes, on medium-low heat.

The Cheese

For the filling, be sure to use a hard Swiss-made cheese such as Gruyère or Emmental – both of which should bear an AOP (Appellation d’Origine Protégée) seal. This sign on the label shows the cheese was made according to strict government mandated rules and quality standards. Both cheeses are subtly salty with lovely nutty notes. They are more pricey than cheddar, but well worth it when used in the filling of this tart.

How to store this Alsatian Onion Tart

After making (and enjoying) this tart– if you have any leftovers – you can store them in the refrigerator or in the freezer.

• In the refrigerator: store it in an airtight container in the fridge for up to 4-5 days. I don’t recommend re-heating it in the microwave, which can make the crust soft. Instead, reheat the tart in the oven for about 5-10 minutes at 350F (180C). 
• In the freezer: store it in a (freezer-friendly) airtight container and place it in the freezer for up to 3 months. To reheat, let the tart thaw in the fridge before heating it through in the oven. 

Cooking notes: 

• The amount of filling in this recipe is just right for low-sided 9-inch (22.9cm) tart pan. Do not fill the crust to the rim: the filling will puff up as it bakes, and deflate slightly as it cools down. It is recommended to use a tart pan with a removable bottom, which will support the crust when lifting your tart.
• It is essential to use cold butter and ice cold water to make the pie crust. Cold butter – not room temperature – will distribute into the flour without softening. And ice-cold water will bind the ingredients together without melting the butter. This ensure little bits of butter are still present in the dough once rolled out, which makes for a flaky crust. 

I hope you’ll love this Alsatian Onion Tart as much as I do! If you have any questions, please leave a comment. 

You may also like:

• Spinach and Cheese Quiche 
• Frisée Salad with Bacon, Egg and Croutons (Salade Lyonnaise)
• Classic French Beef Bourguignon
• Belgian Endive and Ham Gratin (Endives Au Jambon)
• Quiche  Lorraine

Alsatian Onion Tart

Print Recipe

Serves: 6-8 Prep Time: 20 Minutes Cooking Time: 40 Minutes 40 Minutes

Nutrition facts: 200 calories 20 grams fat

Rating: 4.3/5

( 4 voted )

Ingredients

For the pie crust:
2 cups (260g) all purpose flour
1 tsp salt
2/3 cup (150g) cold unsalted butter, cut into small cubes
4 tbsp (60ml) ice cold water

For the filling:
4 tbsp (57g) unsalted butter
2 lbs (900g) onions (yellow or white), peeled and sliced in half rounds
¼ tsp salt
¼ cup (60ml) beef stock (ideally, low-sodium)
3 large eggs
3/4 cup (190ml) heavy cream (35% m.f.)
½ tsp freshly ground black pepper
1/2 cup (2oz/50g) shredded Swiss cheese (ie. Gruyère)
Salt, pepper to taste
1 tsp caraway

Instructions

Step 1: make the crust – Mix the flour, salt and butter with your fingers or pulse in a food processor, until you get a crumbly consistency and pea-size bits of butter are still visible. Add the water, one tablespoon at a time, and mix until the dough roughly comes together into a ball; do not overmix. Add a few more splashes of water if you feel the dough is too crumbly/dry. Wrap the dough in plastic wrap and chill for at least 30 minutes.

Pre-heat your oven to 350°F (180°C) with a rack in the middle.  

Grease and flour a 9-inch (22.9 cm) tart pan. Transfer the dough onto a floured working surface and roll it out to a 12-inch (31cm) circle. Transfer the crust to the tart pan. Cut any excess crust that hangs over the edges and crimp the edges (optional). Poke the bottom of the crust all over with a fork. Line the top of the crust with foil or parchment paper and place pie weights or dried beans over top, to keep the pie crust from puffing when baking.

Bake the crust for 15 minutes. Carefully remove the parchment paper filled with weights and set the crust aside. Leave your oven on at 350°F (180°C).

Step 2 : Caramelize the onions – Melt the butter in a large frying pan over medium-low heat. When the butter is sizzling, add the onions slices and stir to coat with the butter. Using a spatula or wooden spoon, spread the onions evenly onto the pan. Let the onions cook for 15 minutes, stirring every 2 minutes. The trick is to let the onions brown – so do not stir too often. But you don’t want to let them burn either.

After 15 minutes, when the onions should start to dry out, add salt and the beef stock. Stir to coat and continue cooking for about 15 more minutes, until the onions are melty and golden. Set aside.

Step 3: Make the filling - In a large mixing bowl, whisk together the eggs and the heavy cream. Add the black pepper and grated cheese. Adjust more seasoning if needed (salt, pepper).

Step 4: Assemble the tart – Scatter the caramelized onions evenly onto the bottom of the pre-baked crust. Pour the prepared liquid filling over top. Sprinkle evenly with the caraway seeds.

Bake for 25 minutes, until the crust starts to become golden - the middle will be slightly wobbly and puffy, and will firm up and deflate as it cools down. Transfer onto a cooling rack and let cool at least 15 minutes before serving. Enjoy it warm or at room temperature.