Gluten Free Caramelized Onion Quiche

Sweet, jammy onions make this Gluten Free Caramelized Onion Quiche taste like it came from a fancy brunch spot. It bakes up in a gluten free crust with a creamy egg custard, and thanks to high protein milk, each slice has around 13g protein.

I grew up having quiche on almost every holiday morning so making a tasty gluten-free quiche to share with you was such a fun experience. I made this version with my Easy Gluten Free Pie Crust because I wanted a quiche that felt special enough for a holiday morning, but would still keep me full until lunch. Most quiche recipes lean on heavy cream, so I used Fairlife milk for extra protein and let the slow-cooked onions with the balsamic vinegar bring the richness... and trust me when I say, it is amazing.

This gluten free caramelized onion quiche pairs perfectly with my Protein Gluten-Free Cottage Cheese Cinnamon Rolls & Cream Cheese Frosting for a sweet and savory spread. If you need something you can prep the night before, my Easy Overnight High Protein French Toast Casserole or my Make Ahead Gluten Free Breakfast Casserole For Christmas Morning are both great make-ahead breakfast casseroles to add to the table.

Why You’ll Love This Gluten Free Caramelized Onion Quiche Recipe

• More protein than your average quiche. Eggs plus high protein milk bring it to around 13g per serving.
• Gluten free. Use my homemade gluten free crust or your favorite store-bought one crust keep the whole quiche gluten-free.
• Big flavor, simple filling. The custard is just eggs, milk, salt, and pepper. The jammy balsamic caramelized onions and truffle cheese add the flavor.
• Perfect for breakfast, brunch and holidays. It slices cleanly and looks so pretty on the table with fresh thyme on top. I often bake this for my husband and other family (and friends) for holiday breakfast or brunches and everyone loves it.
• Easy to customize. Add other veggies or protein, swap the shredded cheese, or keep it classic. Quiche is one that you can add or take away the fillings and still get something delicious.

Gluten Free Quiche Ingredients (& Tested Substitutions)

Gluten Free Crust

• 9- inch gluten-free pie crust. I make my pie crusts when I can because homemade just tastes so much better, but you can also do store-bought gluten free pie crust that fits a 9-inch pie tin.

Caramelized Onion Mixture

• Onion & Shallot. The onion gives you that classic caramelized flavor and the shallot adds a little extra sweetness. If you don't have a shallot, you can use all onion. I recommend a yellow onion for this recipe but white onion would work well too.
• Unsalted butter. I like to use Plugra butter best, but any unsalted butter works for this recipe.
• Balsamic vinegar. Just a couple teaspoons adds a sweet, tangy depth to the onions.

Quiche Filling

• Eggs. Every quiche uses eggs so no substitute for this.
• Fairlife milk. This is how I bump up the protein. You can use any high protein milk of choice but I like Fairlife best. You can also use whole milk or half and half if you don't care for the higher protein intake.
• Shredded cheese. I used a cheddar gruyère black truffle blend, and it's incredibly delicious here. Plain gruyère, Swiss, or white cheddar are all great swaps.
• Salt & Black pepper. Simple, but don't skip them in the custard.
• Mushrooms. Thinly sliced mushrooms on top add an earthy, cozy flavor that pairs perfectly with the truffle cheese. These are optional though so if you don't like mushrooms, just don't add any.
• Fresh thyme leaves. Sprinkled on top before baking for that fresh, herby finish. Dried thyme works too, just use a little less.

Gluten Free Caramelized Onion Quiche Step by Step Instructions

1. Make pie crust (if you are making from scratch. Make or buy your gluten-free pie crust and put it in a 9-inch pie tin. Set aside in the fridge until you are ready to par-bake it.

2. Caramelize the onions. Melt the butter in a skillet over medium-low heat. Add the sliced onion and shallot and cook, stirring occasionally, for about 30 to 40 minutes until soft, deeply golden, and jammy.

3. Add the balsamic. Stir in the balsamic vinegar for the last 10 minutes of cooking and let it reduce into the onions. Set aside.

4. Parbake the crust. Preheat the oven to 375°F. Line the crust with parchment, fill with pie weights or dried beans, and bake for 15 minutes. Remove the weights and parchment and bake 5 minutes more, until the bottom looks dry. Lower the oven to 350°F.

5. Add the cheese. Sprinkle the shredded cheese evenly over the bottom of the parbaked crust.

6. Make the custard. Whisk the eggs, milk, salt, and pepper together until smooth.

7. Fill the quiche. Pour the egg mixture over the cheese, then spread the caramelized onions on top. Add the sliced mushrooms if using, and finish with fresh thyme.

8. Bake. Bake for about 35 minutes, until the center is set with just a slight jiggle. If the crust edges brown too quickly, cover them with foil or a pie shield.

9. Rest and serve. Let the quiche cool for 10 minutes before slicing so it sets up cleanly.

Gluten Free Quiche Expert Tips & Tricks

• Low and slow on the onions. Keep the heat at medium-low and give them the full 30 to 40 minutes. Rushing cooking the onions on high heat burns them before they get sweet and jammy. This step does take the longest, but it is SO WORTH IT.
• Add the balsamic at the end. Stir it in for the last 10 minutes so it reduces into the onions instead of scorching.
• Don't skip the parbaking. Pouring wet custard straight into raw pastry leads to a soggy bottom. Partially bake the crust first using pie weights or beans.
• Cheese goes on the bottom. Sprinkling it over the crust first creates a little layer between the custard and the crust.
• Avoid overfilling the shell: Filling the quiche custard right to the top causes the custard to spill over the sides as it puffs up in the oven. Leave about half an inch of space at the top.
• Look for a slight jiggle. Leaving the quiche in the oven until it is completely firm throughout makes the eggs rubbery. You will know when the quiche is done when the center is set but still has just a little wobble when you slightly jiggle the quiche. It finishes setting as it rests.
• Protect the edges. If the crust is browning too fast, cover the edges with foil (with the shiny side outward) or a pie shield.
• Let it rest. Give the quiche 10 minutes before slicing so you get clean, pretty slices.

Gluten Free Caramelized Onion Quiche FAQs

Can I use a store-bought crust?

Yes! Any 9 inch gluten free flakey pie crust works. Just make sure to check the label before using.

Do I really need to parbake the crust?

Yes, and honestly it's worth the extra 20 minutes. It's what keeps the bottom crisp instead of soggy under the custard.

What can I use instead of pie crust for quiche?

While I do recommend using a typical flakey pie crust for a quiche, you can also do a crustless approach for this quiche and make it more of a frittata. You could also use gluten free puff pastry dough, though the baking time would be different and I personally haven't tested this recipe with a gluten-free puff pastry specifically.

How do I know when the quiche is done?

After about 35 minutes, the center should be set with just a slight jiggle. It firms up the rest of the way while it cools.

Can I make the caramelized onions ahead of time?

Yes, and it makes this recipe so much faster. Store them in an airtight container in the fridge for up to 3 days, then layer them in when you're ready to bake.

How to Store & Reheat Leftover Quiche 

Cover and refrigerate leftover quiche in an airtight container for up to 3 to 4 days. Reheat slices in a 350°F oven until warmed through, or for a quicker reheat, you can microwave a single slice for about a minute.

If you liked this quiche recipe, you might also enjoy...

• Easy Gluten Free Pie Crust with an Apple Chai Filling (uses my same pie crust recipe)
• Easy High Protein Cottage Cheese Egg Bake Casserole
• Easy Overnight Everything Bagel Breakfast Casserole
• Kale & Mushroom Egg Bites (Starbucks Copycat Recipe)
• Quick & Easy Air Fryer Breakfast Sausage
• How to Cook Breakfast Sausage Patties in the Oven

Did you have a chance to make this recipe? If so, please leave me a 5 star rating and review below. I always love and appreciate hearing from you!