Caramelized Onion and Mushroom Tartlets Recipe

Hey there! Today, we’re taking a savory journey with one of my absolute favorite appetizers: Caramelized Onion and Mushroom Tartlets! These little bites pack a punch with their buttery, flaky crust, sweet caramelized onions, and earthy mushrooms—all topped with a sprinkle of cheese for the perfect finishing touch. Whether you’re hosting friends or simply looking for a delightful appetizer to wow your taste buds, these tartlets are a must-try.

If you’re craving something bite-sized and dangerously delicious, these tartlets have your name on them!

Why You’ll Love This Recipe

Elegant & Festive: These tartlets are the perfect addition to any holiday or party spread, but they’re easy enough to whip up for a cozy night in.
Make-Ahead Friendly: You can prep ahead, making it a stress-free addition to your menu.
Versatile: Not a fan of mushrooms? These are easy to customize, and I’ll show you how!
Minimal Ingredients: You probably already have most of these in your pantry, and if not, I’ve got some quick swaps!

Ingredients Breakdown

For the Tartlet Shells

1 package puff pastry (defrosted)
1 egg (lightly beaten, for egg wash)

For the Filling

2 large onions (thinly sliced)
8 oz mushrooms (sliced, cremini or button mushrooms work great)
2 tbsp butter
1 tbsp olive oil
1 tsp fresh thyme leaves
Salt and pepper to taste
2 oz Gruyere or Parmesan (grated, optional)

Pro Tips:

If you don’t have puff pastry on hand, store-bought pie crust works in a pinch. It won’t be as flaky, but still delicious!
Fresh thyme is wonderful here, but dried thyme is totally fine—just use half the amount.
Mushrooms release a lot of moisture, so be sure to give them plenty of space when you sauté. If the pan is overcrowded, they could steam instead of brown.

Step-by-Step Instructions

Step 1: Prepare the Puff Pastry

Preheat your oven to 400°F (200°C). On a floured surface, roll out your puff pastry to a 1/8-inch thickness. Using a round cutter (or an upside-down glass), cut circles of pastry and gently press them into a mini muffin tin to form the tartlet shells. Brush them lightly with your egg wash and chill in the fridge while you work on the filling. This will help the pastry stay crispy later!

Step 2: Caramelize the Onions

In a large skillet, melt butter with olive oil over medium heat. Add the sliced onions with a pinch of salt and cook, stirring occasionally, for about 20-25 minutes, or until they are soft and golden brown. The key here is patience! Lower the heat if they start to brown too quickly—you want a slow caramelization to bring out the onions’ sweetness.

Step 3: Sauté the Mushrooms

Once the onions are caramelized, transfer them to a plate. In the same skillet, add your sliced mushrooms. Cook them over medium-high heat until they’ve released their moisture and have a beautiful golden sear, about 8-10 minutes. Stir in the fresh thyme and return the caramelized onions to the pan. Season everything with salt and pepper and stir to combine.

Step 4: Fill & Bake

Spoon small amounts of the onion and mushroom mixture into each puff pastry tartlet shell. Top with a sprinkle of Gruyere or Parmesan, if using. Bake in the preheated oven for 15-20 minutes, or until the puff pastry is golden and crisp.

Step 5: Serve & Enjoy!

Allow to cool for just a few minutes before serving—they’ll be hot! These tartlets are delicious straight out of the oven but are equally flavorful at room temperature.

Chef’s Tips and Tricks

No Puff Pastry? Try using phyllo dough for an ultra-light, crispy tartlet. Brush each layer with a bit of melted butter before stacking them together.
Avoid Overstuffing: You don’t need too much filling in each tartlet; keep them light to allow that flaky puff pastry to really shine!
Make-Ahead Hack: Caramelize the onions and cook the mushrooms up to 2 days in advance. Store them in the fridge, then just assemble and bake when ready.

Recipe Variations and Serving Suggestions

Vegetarian Option: Switch up the filling by adding some creamy goat cheese or roasted red peppers.
Meat Lover: Add crispy bacon bits or pancetta to the sautéed mushrooms for an extra savory kick.
Serving Ideas: These tartlets are perfect as an appetizer for a holiday party, or serve them alongside a fresh green salad for a light lunch.
Garnish: Sprinkle with fresh chopped parsley or chives just before serving for a pop of color and freshness.

FAQs

Can I make these tartlets ahead of time?

Yes! You can make the filling up to 2 days in advance and store it in the fridge. To keep the puff pastry fresh and crispy, bake the tartlets just before serving.

Can I freeze these tartlets?

Absolutely. After baking, let the tartlets cool completely, then freeze them in an airtight container for up to 1 month. To reheat, pop them in the oven at 375°F until warmed through.

What if I don’t have mini muffin pans?

No problem! You can make slightly larger tartlets using regular muffin tins or even cut your puff pastry into squares and bake them on a baking sheet for a more rustic look.