Mushroom Onion Tart (Printable)

A savory tart with caramelized onions and mushrooms in a flaky pastry crust, perfect for a light meal or appetizer.

# What You'll Need:

→ Pastry

01 - 1 sheet (8.8 oz) ready-rolled puff pastry or homemade shortcrust pastry

→ Vegetables

02 - 2 tablespoons olive oil
03 - 1 tablespoon unsalted butter
04 - 2 large yellow onions, thinly sliced
05 - 14 oz cremini or button mushrooms, sliced
06 - 2 garlic cloves, minced
07 - 1 teaspoon fresh thyme leaves or ½ teaspoon dried thyme
08 - Salt and freshly ground black pepper, to taste

→ Filling

09 - 3.5 oz crème fraîche or sour cream
10 - 2 large eggs
11 - ¼ cup whole milk or cream
12 - ½ cup grated Gruyère or Swiss cheese

→ Garnish

13 - Fresh parsley, chopped (optional)

# How To Make It:

01 - Preheat oven to 400°F. Line a 9-inch tart pan with the pastry sheet, trimming any excess. Prick the base with a fork and chill in the refrigerator.
02 - Heat olive oil and butter in a large skillet over medium heat. Add sliced onions and cook, stirring frequently, until softened and golden, about 15 minutes.
03 - Add mushrooms to the skillet and cook until tender and all moisture evaporates, approximately 8 to 10 minutes.
04 - Stir in minced garlic and thyme, cooking for an additional minute. Season with salt and pepper to taste, then remove from heat and let cool slightly.
05 - In a mixing bowl, whisk together crème fraîche, eggs, and milk. Fold in half of the grated cheese and season lightly with salt and pepper.
06 - evenly spread the mushroom and onion mixture over the chilled pastry base. Pour the custard filling on top, then sprinkle with the remaining cheese.
07 - Bake for 30 to 35 minutes until custard is set and the top is golden brown.
08 - Allow tart to cool for 10 minutes, garnish with chopped parsley if desired. Slice and serve warm or at room temperature.

# Tips from dashanddishes:

01 -
  • The onions become sweet and golden brown, like edible caramel that nobody expects from something so simple
  • It feels restaurant-worthy but comes together in just over an hour, making you look like a culinary genius without the stress
  • Works beautifully as an elegant appetizer, a light lunch, or even served at room temperature for gatherings
  • Naturally vegetarian but so rich and satisfying that nobody misses meat
02 -
  • Don't skip the pricking step on the pastry. A bubble in the base creates a disappointing pocket that ruins the texture. This lesson came from experience.
  • The onions truly need 15 minutes of patient cooking. Rushing them on high heat gives you soft onions, but slow cooking at medium heat gives you that deep, complex sweetness that makes people ask for your secret
  • Make sure the mushroom liquid completely evaporates. Any excess moisture will make your custard watery and ruin the crispy pastry base
  • Add your garlic last and cook it minimally. Burnt garlic tastes bitter and will overpower the delicate balance you've created
03 -
  • Toast your tart pan in the oven for a few minutes before adding pastry. This helps the bottom cook more evenly and prevents a soggy base
  • Let your cooked tart rest at room temperature for at least an hour before serving. The flavors meld and develop even more richness as it sits
  • Make the mushroom and onion mixture the day before. Storing it in the refrigerator lets the flavors deepen overnight, and you'll have less to do on cooking day

Return