This Alsace onion tart has a flaky, tender pastry shell with a custard filling of rich and creamy caramelized onions and a hint of thyme. It can be served at room temperature as an appetizer but also it is a wonderful entrée served hot for dinner with a salad and a warm, crusty loaf of bread. And, of course, a nice glass of Chardonnay would be lovely.

A serving of French onion tart on a plate with a fork. Green salad in the background.

This is an easy recipe but don’t rush the process for cooking the onions. Let them caramelize low and slow until they practically melt. It makes all the difference. You can simplify the process by cooking the onions a day in advance and even use store-bought pastry if you don’t want to make your own. Either way, this Alsatian onion tart is sure to please.

Overhead view of a baked French onion tart in the baking pan.

Don and I are a part of a small group of church friends that meet each Tuesday night for a bible study. At the end of the year, we always have a potluck Christmas party.

My contribution to the menu is this Alsace onion tart, (also called tarte à l’oignon Alsacienne). Alsace is the smallest French region located in the northeast corner of France. This is one of the areas we visited in 2009, and it is well known for its Alsatian wines and great food.

Alsatian Onion Tart

This tart recipe is straightforward and easy to make. The savory custard filling is quite rich and you only need a small slice. It makes a fantastic appetizer but it is also perfect for dinner, as a brunch entree, or a lazy breakfast.

The recipe is similar to our leek and bacon quiche but a bit more rustic. If you enjoy this Alsace onion tart, you will like our mushroom and goat cheese quiche and our smoked salmon quiche or our sweet Walla Walla onion quiche.

Ingredients for our Alsatian Onion Pie

The pastry:

Flour. All purpose flour.
Butter. Butter gives the crust a rich flavor.
Salt.
Water. Make sure the water is ice cold.
Vinegar. This helps prevent gluten development and keeps the crust tender and flakey.

The filling:

Bacon
Onions
Salt and pepper
Cream
Eggs
Nutmeg and thyme
Gruyere cheese

How to Make an Alsatian Onion Tart

Here is a quick overview of the recipe. Make sure to scroll down to the recipe card for all the details.

Combine the ingredients for the pastry. Roll it out and place it in an 11-inch tart pan then pre-bake the crust.
Cook the bacon until crispy.
Saute the onions until soft, sweet and caramelized.
Whisk the rest of the filling ingredients together then stir in the onions and bacon.
Pour the filling into the tart shell, sprinkle the cheese over the top, then bake.

Tips for Success with this French Onion Tart:

Cook the bacon and onions up to 2 days in advance to save some time.
Make the pastry in advance. You can wrap the dough in plastic wrap and keep it in the freezer for several months. You can also bake it crust up to 2 days in advance.
Take your time when you cook the onions. If you want to add a little extra flavor, follow our recipe for caramelized onions. We use a splash of white wine and some herbs in that recipe.
Make an extra-large batch of the onions to use in other recipes like our bruschetta with caramelized onions and our baked eggs.

A baked onion tart on a wooden cutting board.

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A sliced French onion tart on a wooden cutting board.

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This recipe was given to me by our friend Randy, the owner of Tucker Cellar’s Winery in the Yakima Valley, WA. It was served as one of the appetizers for a wine-tasting event earlier this year.

Alsace Onion Tart (Tarte à l’Oignon)

If you're looking for a tart that truly embodies richness and luxury, this Alsace Onion Tart, also known as a French Onion Tart, is for you.

With a golden, buttery crust and a creamy filling bursting with tender onions, smoky bacon, and aromatic thyme, this dish is pure comfort. Topped with a generous sprinkle of grated Gruyère cheese, this is an indulgent dish.

Serve it as a main meal for lunch, dinner, or brunch, or slice it into smaller portions and serve it as an appetizer.

4.69 from 22 votes

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Prep Time: 1

Cook Time: 45

Total Time: 1 45

Servings: servings

Calories: 193kcal

Author: Pat Nyswonger

Ingredients

For pastry

2 cups all-purpose flour plus more for dusting
¾ teaspoon salt
1-½ sticks of cold butter cut into cubes
5 tablespoons ice water
1 teaspoon cider vinegar

For filling

4 bacon slices 1/4 lb, cut crosswise into ⅛- to 1/16-inch-wide strips
2 lb onions halved lengthwise and very thinly sliced crosswise (10 cups)
1-¼ teaspoons salt
1 teaspoon black pepper
1 cup heavy cream
4 extra large eggs
2 egg yolkes
½ teaspoon freshly grated nutmeg
2 tablespoons minced fresh thyme
½ cup grated Gruyere cheese

Instructions

Blend flour and salt together in a large bowl. Cut in the butter using a pastry blender (or pulse in a food processor) just until most of mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Mix the vinegar and 5 tablespoons of ice water together and drizzle evenly over the flour mixture and gently stir with a fork
Squeeze a small handful: If it doesn’t hold together, add more ice water, ½ tablespoon at a time, stirring (or pulsing) until just incorporated, then test again. (Do not overwork mixture, or pastry will be tough.)
Turn out mixture onto a lightly floured surface. Gather dough together with pastry scraper and press into a ball, and then flatten into a disk. Chill dough, wrapped in plastic wrap, until firm, at least 1 hour.
Roll out dough on a floured surface with a floured rolling pin into a 15-inch round and fit into a 11″ tart pan, lifting and gently pressing into the pan. Trim excess dough, leaving a ½-inch overhang, then fold overhang over pastry and press against side to reinforce edge. Lightly prick bottom with a fork and chill until firm, about 30 minutes. (If using a tart pan with a revomable bottom place the pan on a baking sheet when putting it into the oven).
Put oven rack in middle position and preheat oven to 400°F.
Line chilled shell with foil and fill with pie weights. Bake until pastry is set and pale golden along rim, 15 to 20 minutes. Carefully remove foil and weights and bake shell until golden all over, 10 to 15 minutes more. Transfer baked shell to a rack to cool. (Reduce oven temperature to 375 degrees)

Filling:

Place the bacon into a cold skillet, and cook over medium heat until browned. Remove bacon from skillet and drain on paper towels, reserve 4 tablespoons of the bacon fat.
Add sliced onions to the skillet with the reserved bacon fat and cook onions with ¾ teaspoon salt and ½ teaspoon pepper over moderate heat, stirring, until just wilted, about 2 minutes. Cover skillet with a lid and continue to cook, stirring frequently until onions are very soft and pale golden, about 20 minutes. Stir in bacon, then remove from heat and cool completely.
Whisk together the cream, eggs and yolks, nutmeg, thyme, remaining ½ teaspoon salt, and remaining ½ teaspoon pepper in a large bowl, then stir in onions.
Pour filling into tart shell, spreading onions evenly, sprinkle ½ cup of grated Gruyere cheese evenly over the top and bake until filling is set and top is golden, 40 to 50 minutes. Serve warm or at room temperature