Recipes › Bulb Onion › Alsatian Onion Tart
Alsatian Onion Tart
Inspired by the tarte flambée of Alsace, this savory tart fills a crisp, buttery pastry shell with a silky custard of slowly cooked onions, crème fraîche, eggs, and gruyère — a sophisticated balance of sweet onion, rich cream, and nutty cheese. It is elegant enough for a dinner party starter and satisfying enough to anchor a light supper alongside a crisp green salad. Prepared in advance and served at room temperature, it is also an ideal make-ahead dish.
Bulb Onion is usually ready June to August. More bulb onion recipes, or see what to sow this month where you are.
Ingredients
- 2½ lbs yellow onions, thinly sliced into half-rings
- 3 tbsp unsalted butter
- ¾ cup crème fraîcheSour cream as a substitute
- 3 large eggs
- 3 oz Gruyère cheese, shredded
- 1 tsp fresh thyme leaves
- 0.13 tsp freshly grated nutmeg
- to taste salt and white pepper
- 1 9-inch pre-made or homemade pie shell, blind-baked for 15 minutes at 375°F
Contains: cereals gluten, milk, eggs.
Method
- Blind-bake the pie shell: line with parchment, fill with pie weights or dried beans, and bake at 375°F for 15 minutes. Remove weights and parchment and bake a further 5 minutes. Set aside. Reduce oven temperature to 350°F.About 25 min
- Melt butter in a large skillet over medium-low heat. Add the sliced onions and 1/2 tsp salt. Cook, stirring every 5 minutes, for 35-40 minutes until very soft, golden, and sweet. Remove from heat and let cool for 10 minutes.About 45 min
- Whisk together the crème fraîche, eggs, thyme, nutmeg, and a pinch each of salt and white pepper. Spread the cooled onions in the blind-baked shell. Scatter the Gruyère over the onions. Pour the custard over the top. Bake at 350°F for 30-35 minutes until the custard is just set with a slight wobble in the center and lightly golden on top. Cool for 15 minutes before slicing.About 35 min
Tips
- Blind-baking the shell prevents a soggy bottom — do not skip this step.
- The tart is best served warm or at room temperature, never piping hot.
- Cooling the onions before adding the custard prevents the eggs from curdling.
Ring the changes
- Add 4 strips of cooked, crumbled bacon (lardons) scattered over the onions for a heartier tart.
- Substitute half the Gruyère with Comté or Emmental for a more nuanced cheese flavor.
Keeping it
Refrigerate for up to 2 days. Serve at room temperature or warmed gently in a 300°F oven for 10 minutes.
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