Mozzarella, Mushroom, and Caramelized Onion Bites Recipe: A Potluck Must

If there is any advice I can give to someone trying to find a recipe to bring to a significant other’s family’s house on holidays, I always recommend appetizers! You don’t know who is bringing main dishes, and you will be everyone’s favorite person when they get the munchies before dinner is served. This recipe for Mozzarella, Mushroom, and Caramelized Onion Bites based on the recipe from Little Spice Jar is perfect. 

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

It is a good bite sized food that is reheatable (if there end up being any left.) On top of that, the bougie name and appearance make them look harder to make than they actually are, which is a must when bringing foods to potluck events like office holiday parties or family dinners.

The first step is to thinly slice your mushrooms and, unfortunately, your onions. If chopping onions affects you as badly as it does me, aka violently sobbing like I read My Sister’s Keeper again to the point of temporary blindness, I do have a tip for you. Freeze your onions for at least half an hour before you cut them up! This will make the juice less likely to spread up through the air and making your vision last a little longer.


Put your onions to the side at this point, and saute your mushrooms in a mixture of oil and butter. When your shrooms are soft, take them out of the pan and put them in a medium sized bowl.

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Next comes the exciting part: caramelizing the onions.

Add a tablespoon of oil and three tablespoons of butter to the pan. (Paula Deen be damned) Let it melt at a medium temp before adding your onions, being careful not to burn your butter. Make sure you have a large enough pan. I read that at least a 12″ pan is needed for two onions to give them room to breath. Understandably.

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Saute the onions until they are see through. Turn the stove down to low-medium and add the thyme and sugar. Here is where I departed from the original recipe some. It said that it should only take 25 minutes to brown, but I would say it’s closer to 45. Stir the onions every five minutes. The trick is to cook them low and slow and leave them on until they are golden brown.

Once the golden brown color has been reached and you’ve spent an acceptable time screeching, “Look!! They caramelized!! I did it!!”, use the balsamic vinegar to declare the pan and let the onions soak it up for more yummy flavor. Remove the onions and put them in the bowl with the mushrooms.


Now is when you have two options. Cover and refrigerate the bowl for up to 48 hours then make your treats, or continue on with the recipe. Because I took them to Thanksgiving and didn’t want to wake up too early, I made the filling the night before and then did this next part in the morning. It’s up to you. But if you do put it in the fridge, let it come to room temperature before you proceed.

Now, mix in the best part: the CHEESE. The original recipe suggests gruyere, but I used mozzarella because ya girl can’t afford no $10 cheese. Gruyere sounds like it would be DELICIOUS though, so you money bags out there should try the original recipe! Anywho, I digress…

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Thaw your puff pastry in the fridge overnight, but make sure it remains cold throughout this process. Cut the pastry into 2×2 squares and lay the squares out on some parchment paper. Brush them with a beaten egg, and put a tablespoon of your filling mixture on top of the pastry.

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Put your pastries in the oven for about 20-25 minutes. Now comes the scary part, especially when you live in a house of asshole cats. Be careful about slamming the oven or slamming doors, dropping things, playing loud music, knocking everything you can off of services, etc. because loud noises or things that cause a lot of vibration can make your pastries fall. They won’t all puffed up and fluffy like they should be.

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Once they come out of the oven, all golden and brown, let them rest and then devour them.


This is the perfect holiday dish! Warm, buttery, sweet, crunchy, cheesy… What more can you ask for, right?!

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

Domesticate Kate | Mozzarella, Mushroom, and Caramelized Onion Bites

How was y’all’s holiday? Mine was a relaxing day full of family, laughs, and football rivalries.

Domesticate Kate

Little Spice Jar's Mozzarella, Mushroom, and Caramelized Onion Bites

  • Servings: About 32 bites
  • Time: Prep Time: 10 mins, Cook Time: 65 mins
  • Difficulty: Easy to Medium
  • Print

The perfect appetizer for a family meal or an office potluck. Sweet, savory, cheesy, and crunchy. Must have addition to your holidays!


  • 4 tbs salted butter, divided
  • 2 tbs vegetable oil, divided
  • 5-6 oz crimini (or baby bella) mushrooms
  • 2 medium yellow onions, thinly sliced
  • 1/4 tsp dried thyme
  • 1 tbs sugar
  • 1 1/2 tsp garlic powder
  • salt and pepper, to taste
  • 4 oz grated mozzarella (or gruyere or swiss) cheese
  • 1 pkg frozen puff pastry, thawed
  • 1 egg, lightly beaten


  1. In a large cast iron skillet over medium heat, heat 1 tablespoon of oil along with 1 tablespoon of butter. Add the mushrooms and sauté for about 5 minutes until tender. Remove and set aside in a medium bowl.
  2. Heat the remaining 3 tablespoons of butter along with the 1 tablespoon of oil and sauté the onions for 5 minutes. Add the dried thyme and sugar and continue to cook for 25 minutes on medium low heat. Make sure to stir the mixture every 5 minutes or so. If the onions are caramelizing too fast, turn down the heat a little more. Add the balsamic vinegar to deglaze the pan, allow the onions to soak it all in. Turn off heat. Add the onions to the mushroom mixture. Season with the garlic powder and salt and pepper to taste, stir to combine. Allow to cool to room temperature. Mixture can be kept in an air-tight container and refrigerated for up to 48 hours at this point. Allow to come to room temperature before proceeding. Add the gruyere cheese and mix well.
  3. Position two racks in the upper and lower thirds of the oven. Preheat the oven to 400 degrees F. Line 2 baking sheets with parchment paper or silicone mats.
  4. Using a knife or a pizza cutter, cut the puff pastry into 2-inch squares and place them on a lined baking sheet. Make sure the puff pastry is cold before proceeding. If not, allow it to rest in the refrigerator for 10-15 minutes before proceeding. Using a pastry brush, brush the beaten egg on the squares. Place a tablespoon of caramelized onion mixture in the center. Bake for 20-25 minutes, rotating the pan halfway in between until crisp and golden brown. Let cool slightly before serving.

Little Spice Jar's Notes

Make sure the puff pastry is cold when it goes into the oven. If at any point it becomes soft, allow it to rest in the refrigerator for 15-20 minutes or until it firms up again. Do not open the oven door during the first 10 minutes of baking time. Frequently opening the oven may cause the puff pastry to not ‘puff up’.

Swiss cheese or gruyere cheese may be used to replace the mozzarella.

If you’ve prepared the caramelized onion mixture ahead of time, you can zap it in the microwave for 30 seconds to bring it back to room temperature quickly.


Another recipe option is Cowboy Caviar Recipe. Check it out!


5 thoughts on “Mozzarella, Mushroom, and Caramelized Onion Bites Recipe: A Potluck Must

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