Mushroom and Onion Tart (Printable Format)
Flaky tart with caramelized onions, sautéed mushrooms, and creamy cheese, great for a light meal or appetizer.
# What You Need:
→ Pastry
01 - 1 sheet (about 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 Steps:
01 - Preheat oven to 400°F. Line a 9-inch tart pan with the pastry, trimming any excess. Prick the base with a fork and refrigerate while preparing the filling.
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 sliced mushrooms to the skillet and cook until softened and moisture evaporates, approximately 8 to 10 minutes.
04 - Stir in minced garlic and thyme, cooking for 1 additional minute. Season with salt and pepper. Remove from heat and allow to cool slightly.
05 - In a bowl, whisk together crème fraîche, eggs, and milk. Mix in half of the grated cheese, seasoning lightly with salt and pepper.
06 - Evenly spread the mushroom and onion mixture over the chilled pastry base. Pour the custard filling over the vegetables and sprinkle remaining cheese on top.
07 - Bake in the preheated oven for 30 to 35 minutes, until the filling is set and the surface is golden brown.
08 - Allow the tart to cool for 10 minutes. Garnish with chopped parsley if desired, slice, and serve warm or at room temperature.
# Expert Suggestions:
01 -
- It looks restaurant-worthy but feels entirely forgiving—even if your pastry isn't perfect, the filling makes it shine
- The caramelized onions are pure umami magic, sweet and deep in a way that makes people ask what your secret ingredient is
- You can make it ahead and serve it warm or at room temperature, making it the ultimate dinner party hero
- It proves that vegetables alone can be the main event, not an afterthought
02 -
- The caramelization of onions cannot be rushed. I learned this the hard way after many batches of onions that stayed pale and sharp. Low and slow is not just advice—it's the entire technique.
- Pricking the pastry base is non-negotiable if you want a crispy foundation. This small act prevents a soggy bottom, which is the one thing that can derail an otherwise perfect tart.
- Letting your assembled tart rest in the refrigerator for at least 15 minutes before baking helps the pastry crisp up and prevents shrinkage. I discovered this after my first tart emerged significantly smaller than I'd hoped.
03 -
- Make your mushroom and onion mixture the day before and refrigerate it. You can then assemble and bake the tart the next day for even easier entertaining.
- If your pastry cracks slightly during fitting, don't stress—you can patch small tears with a small piece of extra pastry and a drop of water. The filling covers imperfections beautifully.