Caramelized Onion Puff Pastry Squares: Your New Go-To Holiday Appetizer

Is there anything more welcoming than the smell of onions slowly caramelizing on the stove? It’s the kind of smell that tells everyone the good food is just getting started. Now, imagine that sweet, deeply savory flavor tucked into a buttery, flaky puff pastry square. I mean, come on. These Caramelized Onion Puff Pastry Squares are the little black dress of holiday appetizers—fancy enough for your Thanksgiving table but so unbelievably easy you can whip them up for any Friendsgiving or last-minute party. They’re the first thing to disappear every single time. So good.

Top Reasons To Make It

You’ll want to keep this recipe in your back pocket for a million reasons. First, it’s seriously easy. Using store-bought puff pastry is a genius shortcut that gives you all the credit. Second, that rich, sweet-and-savory onion filling feels gourmet but is made with simple, humble ingredients. And finally, they are the ultimate make-ahead appetizer. You can prepare the filling days in advance, so when company arrives, all you have to do is assemble and bake. They free up your time so you can actually enjoy your own party.

Ingredients

• 2 large yellow onions, thinly sliced: The star of the show, they’ll cook down into sweet, jammy perfection.
• 2 tbsp unsalted butter: For sautéing and adding rich flavor.
• 1 tbsp olive oil: Helps the butter from burning and adds depth.
• 1 tsp brown sugar: A little cheat to help the caramelization along beautifully.
• 1/4 cup beef or vegetable broth: Deglazes the pan and adds a savory backbone (we’re skipping the wine!).
• 1 tsp balsamic vinegar: Adds a touch of acidity and complexity.
• 1/2 tsp dried thyme: That classic, cozy herb that pairs perfectly with onion.
• 1 sheet frozen puff pastry, thawed: The effortless, flaky vessel for our delicious filling.
• 1 egg, beaten: For that gorgeous, golden-brown shine on top.
• Coarse sea salt and black pepper: To taste, for seasoning every layer.

Instructions

1. Caramelize the onions: In a large skillet over medium-low heat, melt the butter with the olive oil. Add the sliced onions and give them a good toss to coat. Cook, stirring every few minutes, for about 20 minutes until they’ve softened and started to turn golden. Don’t rush this part! Sprinkle with the brown sugar and continue cooking for another 10-15 minutes, until they are a deep golden brown and jammy.
2. Deglaze the pan: Pour in the broth and balsamic vinegar. Use your spoon to scrape up all those delicious browned bits from the bottom of the pan. Stir in the thyme and season generously with salt and pepper. Let it cook for another 2-3 minutes until the liquid has mostly evaporated. Remove from heat and let this mixture cool completely. Honestly, you can even do this step a day or two ahead—it makes assembly a breeze.
3. Prepare the pastry: Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper. Unfold your thawed puff pastry sheet onto a lightly floured surface. Gently roll it out just enough to smooth any creases. Cut the sheet into 9 or 12 equal squares.
4. Assemble the squares: Spoon a heaping tablespoon of the cooled onion mixture onto the center of each pastry square. Fold each corner of the square toward the center, overlapping them slightly—they don’t have to be perfect! Give them a little press in the middle so they hold their shape.
5. Bake: Place the assembled squares on your prepared baking sheet. Brush the tops and visible pastry with the beaten egg. This is the secret to that beautiful, professional-looking shine. Bake for 15-18 minutes, or until the pastry is puffed and a glorious, deep golden brown. Let them cool on the sheet for just a minute before serving—that filling is hot!

Perfect Pairings For Holiday Appetizers

These squares are fantastic on their own, but they also love company. They’re a wonderful addition to any Thanksgiving charcuterie board, sitting right alongside some sharp cheeses, cured meats like smoked turkey, and fresh fruit. For a creamy contrast, serve them with a dollop of garlic herb dip or a simple spread of whipped goat cheese. And if you’re putting out a spread of holiday appetizers, they play nicely with other easy finger foods like baked brie with jam or roasted red pepper pinwheels.

Variations & Substitutions

This recipe is a wonderful canvas for your own ideas. Want to make it vegetarian? Just stick with vegetable broth. For a cheesy twist, sprinkle a little Gruyère or Parmesan into the center with the onions before you fold the pastry over. If you have fresh herbs, swap the dried thyme for a teaspoon of fresh chopped rosemary. And if you’re a mushroom lover, sauté some finely chopped cremini mushrooms with the onions for an even deeper, earthier flavor. So many possibilities.

Serving Ideas For Thanksgiving Gatherings

I love setting these out the moment guests arrive. The aroma alone makes people feel welcome. Arrange them on a beautiful platter garnished with a few fresh thyme sprigs. For a Friendsgiving potluck, these are the perfect travel-friendly app—just bake them at home, cover loosely with foil, and they’ll still be delicious at room temperature. They’re the ideal bite-sized starter that won’t spoil anyone’s appetite for the big meal.

Storage & Reheating

If you have leftovers (a rare occurrence in my house!), you can keep them in an airtight container in the fridge for up to 3 days. The best way to reheat them and bring back that flaky texture is in the oven. Pop them on a baking sheet in a 350°F (175°C) oven for about 5-8 minutes, until warmed through. I don’t recommend the microwave, as it will make the pastry soft. You can also freeze the unbaked assembled squares on a baking sheet until solid, then transfer to a freezer bag. Bake from frozen, adding a few extra minutes to the baking time.

Frequently Asked Questions

• Q: Can I make the onion filling ahead of time?
  A: Absolutely! In fact, I recommend it. The caramelized onion mixture can be stored in an airtight container in the refrigerator for up to 3 days. This makes assembly on the day of your party super fast.
• Q: My puff pastry is frozen solid. How do I thaw it?
  A: The safest way is to move it from the freezer to the refrigerator the night before you need it. If you’re short on time, you can leave it on the counter for about 30-40 minutes. Just don’t use a microwave, or it’ll get sticky and hard to work with.
• Q: Are these a good make-ahead appetizer for Christmas?
  A: They are one of the best Christmas appetizers because you can do almost all the work in advance. Prep the filling and even assemble the squares a day ahead. Keep them covered on the baking sheet in the fridge, then just brush with egg and bake when you’re ready.