If you’re looking for something cheesy, crispy, and totally delicious, you’re in the right place. Today, I’m sharing one of my all-time favorite tarts, Caramelized Onion Mushroom Tart with Cheddar Mornay Sauce. It’s savory, buttery, and packed with flavor. Plus, it smells amazing while baking!
Whether you’re hosting a brunch, need a fancy snack, or want a cozy dinner with a salad on the side, this tart is always a winner.
Method
Pancetta Time
To kick things off, grab a skillet and place it over medium heat. Add the pancetta and let it cook until the pieces turn golden brown and crispy. This will take just a few minutes, and you’ll notice the fat rendering out beautifully. Once it’s nice and crispy, transfer the pancetta to a paper towel-lined plate to drain. Don’t clean the skillet yet we’re going to build even more flavor in the next step using that delicious leftover fat.
Make the Sweet & Savory Veggies
In the same skillet, lower the heat slightly and add ½ tablespoon of butter. Once it melts, toss in the thinly sliced red onions along with a teaspoon of sugar. Stir them gently and let them cook low and slow for about 10 minutes. The sugar helps speed up the caramelization, making the onions sweet and jammy. When they’ve softened and turned golden, add the sliced cremini mushrooms. Cook the mushrooms for about 6 minutes until they shrink and turn a rich brown. Now, add the chopped thyme, nutmeg, salt, and white pepper. Stir everything together and cook for an additional 2 minutes to let the flavors come together. The aroma at this point is truly mouthwatering!
Prepare the Puff Pastry
Next, it’s time to get the base ready. Take your thawed puff pastry sheet and place it on a parchment-lined baking sheet. Using a sharp knife, lightly score a ½-inch border around the edges be careful not to cut all the way through. This border will puff up in the oven, giving your tart a beautiful edge. Then, use a fork to poke holes all over the center section. This step is called “docking,” and it keeps the middle from puffing up too much while baking. Brush the entire pastry especially the edges with the egg wash (just one egg whisked with a tablespoon of water). Now, place the pastry in a preheated oven at 400°F and blind bake it for 12 minutes, or until the edges are starting to puff and look lightly golden.
Let’s Make Cheese Sauce!
While the pastry is in the oven, make the delicious Cheddar Mornay sauce. In a clean skillet or small saucepan, melt ½ tablespoon of butter over medium heat. Once melted, whisk in the flour and let it cook for about 2 minutes. This helps remove the raw flour taste and forms a simple roux. Now, slowly pour in the milk while continuously whisking. You’ll notice it begins to thicken this is exactly what you want! Once it reaches a smooth, creamy consistency, take the skillet off the heat. Stir in the grated Black Creek Cheddar with Gruyere and Parmesan cheeses, along with a pinch of nutmeg, salt, and black pepper. Mix until everything is melted and velvety. This cheesy sauce will be the flavorful foundation of your tart.
Assemble the Tart
Once the puff pastry has finished its blind bake, remove it from the oven and let it cool slightly. Then, using a spoon or offset spatula, spread the warm Mornay sauce evenly over the center of the tart, making sure to stay inside the scored border. Next, sprinkle half of the grated cheese over the sauce, creating a cheesy base for the toppings. Add the caramelized onion and mushroom mixture evenly across the tart. Then, sprinkle the remaining grated cheeses right on top for a super melty finish. Finally, scatter the crispy pancetta pieces across the top it adds a perfect salty crunch to every bite.
Final Bake
Return the assembled tart to the oven and bake for another 8 minutes at 400°F. Keep an eye on it as the cheese melts and bubbles, and the edges of the pastry turn a beautiful golden brown. Once everything is perfectly baked and golden, take it out of the oven and let it rest for a couple of minutes. Sprinkle a little fresh thyme on top for that final pop of flavor and color. Then, slice it up and serve warm it’s pure cheesy, savory goodness in every bite!
Necessary Tools
- Skillet (non-stick or stainless steel)
- Spatula or wooden spoon
- Cheese grater
- Sharp knife
- Baking sheet
- Parchment paper
- Pastry brush (for egg wash)
- Whisk
Caramelized Onion Mushroom Tart
Cuisine: FrenchDifficulty: Easy6
servings20
minutes30
minutes50
minutesIngredients
For the Tart
1 sheet puff pastry (thawed)
6 oz cremini mushrooms, sliced
½ medium red onion, thinly sliced
3 oz pancetta
1½ cups Black Creek Cheddar with Gruyere, grated
½ cup Black Creek Cheddar with Parmesan, grated
½ tbsp fresh thyme, chopped
1 tsp sugar
¼ tsp salt
¼ tsp white pepper
¼ tsp nutmeg
½ tbsp butter
Cheddar Mornay Sauce
½ tbsp butter
½ tbsp flour
½ cup + 2 tbsp milk
¼ cup each of Black Creek Cheddar with Gruyere and Parmesan
¼ tsp nutmeg
¼ tsp salt
⅛ tsp black pepper
Egg Wash
1 egg + 1 tbsp water
Directions
- Pancetta Time
Start by cooking your pancetta in a skillet until it’s golden and crispy. Set it aside on a paper towel. It adds a yummy salty crunch later! - Make the Sweet & Savory Veggies
In the same skillet, melt butter and add your thin red onion slices with sugar. Cook them low and slow for 10 minutes until they caramelize and turn soft and sweet. Add mushrooms and cook for 6 minutes. Then add thyme, nutmeg, salt, and pepper, and cook 2 more minutes. Smells soooo good, right? - Prepare the Puff Pastry
Roll out your puff pastry on a baking sheet lined with parchment paper. Use a knife to score a border ½-inch from the edge (this will puff up and look fancy!). Poke some holes in the middle using a fork so it doesn’t puff up too much. Brush with the egg wash and blind bake for 12 minutes at 400°F. It should look slightly golden. - Let’s Make Cheese Sauce!
In a clean skillet, melt the butter, then whisk in the flour. Cook for 2 minutes. Slowly pour in the milk while whisking. Let it thicken up like magic! Take it off the heat and stir in the cheeses, nutmeg, salt, and pepper until melty and creamy. - Assemble the Tart
Spread that cheesy Mornay sauce on the center of the puff pastry. Add half the shredded cheese, then the mushroom-onion mix, then sprinkle the rest of the cheese. Don’t forget to top it with crispy pancetta! - Final Bake
Pop it back in the oven for 8 more minutes until the cheese is bubbly and the tart is golden brown. Sprinkle some extra thyme on top if you’re feeling fancy.
Notes
- Don’t skip poking holes in the puff pastry this keeps the middle from puffing too high.
- Make sure to cook the flour in the sauce for at least 2 minutes to avoid a raw flour taste.
- Be careful not to burn the onions caramelizing takes time and patience!
- Add cheese gradually in the sauce so it melts smoothly, not in clumps.
- Blind baking is important! It gives the tart a crispy bottom so it’s not soggy.
Serving Suggestions
- Pair it with a simple green salad with lemon vinaigrette.
- Slice it into smaller squares and serve as an appetizer for guests.
- Enjoy it with a warm bowl of soup for a cozy meal.
- Great for brunch, lunch, or even as a side for dinner!
Fun Fact
Did you know? Mornay sauce is just a fancy name for cheese sauce! It’s a cousin of béchamel (white sauce) but with cheese added in. The French really know how to make things sound delicious!
Conclusion
And there you have it your very own Caramelized Onion Mushroom Tart! This recipe is bursting with cozy, savory flavors and creamy cheesy goodness. Perfect for impressing guests or just treating yourself (you deserve it!). I hope you enjoy making it as much as I do. Let me know how it turns out in the comments!
