Sweet Caramelized Onion Tart

Name: Sweet Caramelized Onion Tart
Prep time: 20 min
Cook time: 40 min
Total time: 1 h
Yield: 8 servings
Ingredients: 1 pie crust (store-bought or homemade); 3 large onions, thinly sliced; 2 tablespoons olive oil; 1 tablespoon butter; 1 teaspoon sugar; Salt and pepper, to taste; 1 tablespoon fresh thyme (optional); 1 cup heavy cream; 3 large eggs

Highlighted under: Warm Plates

I absolutely adore creating savory tarts, and this Sweet Caramelized Onion Tart has become one of my favorites. The combination of sweet, slowly caramelized onions with a flaky crust captures a depth of flavor that’s truly irresistible. I love serving this tart at gatherings, as it brings a touch of elegance and comfort to the table. Whether enjoyed warm or at room temperature, it’s perfect for a light lunch or as an appetizer. Trust me, once you try this recipe, you'll find yourself making it over and over again.

Created by

Emily

Last updated on 2026-01-08T13:47:31.851Z

When I first made this Sweet Caramelized Onion Tart, I knew I wanted to highlight the onions' natural sweetness. The key is patience while caramelizing the onions; it takes time, but the reward is worth every minute. I learned to control the heat so they soften without burning, allowing their natural sugars to develop beautifully.

This tart has since enchanted my friends and family. What I adore is how versatile it is. Adding herbs like thyme or a sprinkle of cheese can elevate the flavors even further, so don't hesitate to experiment with what you have on hand!

        Why You'll Love This Tart
        Savory sweetness that tantalizes the taste buds
Flaky, buttery crust that perfectly complements the filling
Versatile enough for any occasion, from brunch to dinner parties

      

The Art of Caramelization

Caramelizing onions is a crucial step that enhances the overall flavor of your Sweet Caramelized Onion Tart. To achieve that perfect golden-brown color and rich sweetness, it's vital to cook the onions slowly over medium heat. Stirring occasionally and being patient during this process is key; rushing can lead to burnt edges rather than sweet, tender onions. Aim for about 30 minutes of cooking time, and don’t be afraid to adjust the heat to avoid scorching.

Using both olive oil and butter not only adds depth to the flavor but also helps in achieving the ideal cooking temperature. The olive oil raises the smoke point, while the butter adds richness. If you don't have olive oil on hand, you can substitute it with vegetable oil, but I find that a combination of fats yields the best results. Keep the salt handy; it helps draw out moisture from the onions, accelerating the caramelization process.

Perfecting the Tart Crust

A flaky, buttery crust is the perfect vessel for your decadent filling. When pre-baking, it’s important to prick the bottom of the pie crust with a fork, which helps prevent air bubbles from forming. Another helpful tip is to use parchment paper with pie weights or dried beans on top during the pre-bake. This additional weight keeps the crust flat and ensures even cooking, avoiding any sogginess later on.

If you're using a store-bought crust, opt for an all-butter variety for the best flavor and texture. Homemade crust is a fantastic option too; I often like to incorporate a pinch of salt and a touch of vinegar into my dough to enhance its flavor and flakiness. Should you want to make it ahead of time, the unbaked dough can be frozen for up to a month. Just be sure to wrap it tightly to prevent freezer burn.

Ingredients

Ingredients for Sweet Caramelized Onion Tart

For the Tart

1 pie crust (store-bought or homemade)
3 large onions, thinly sliced
2 tablespoons olive oil
1 tablespoon butter
1 teaspoon sugar
Salt and pepper, to taste
1 tablespoon fresh thyme (optional)
1 cup heavy cream
3 large eggs

Instructions

Prepare the Crust

Preheat the oven to 400°F (200°C). Roll out the pie crust and fit it into a tart pan. Prick the bottom with a fork to prevent bubbling.

Pre-bake the crust for 10 minutes until lightly golden. Remove from oven and set aside.

Caramelize the Onions

In a large skillet, heat olive oil and butter over medium heat. Add the sliced onions, sugar, salt, and pepper. Cook, stirring occasionally, for about 30 minutes until the onions are deeply caramelized.

Make the Filling

In a bowl, whisk together the cream, eggs, thyme (if using), and a pinch of salt. Fold in the caramelized onions, mixing well.

Assemble and Bake

Pour the onion mixture into the pre-baked tart crust. Bake in the oven for an additional 30 minutes or until the filling is set and slightly golden on top. Allow to cool before serving.

Pro Tips

For an extra touch, sprinkle grated cheese on top before baking or try adding a pinch of nutmeg for added warmth.

Serving Suggestions

This Sweet Caramelized Onion Tart can be enjoyed warm or served at room temperature, making it a versatile dish for any gathering. Consider pairing it with a simple arugula salad drizzled with lemon vinaigrette to balance the tart's rich flavors. You can also offer a side of herbed cream cheese or a tangy goat cheese spread to elevate the experience even further; they complement the onion's sweetness beautifully.

For a more substantial meal, serve it alongside a hearty soup, like tomato basil or butternut squash. The contrasting textures and flavors will delight your palate, transforming it into a delightful lunch or dinner option. If you're feeling creative, consider adding sautéed mushrooms or spinach to the filling for added flavor and nutrition.

Make-Ahead and Storage Tips

The Sweet Caramelized Onion Tart is an excellent make-ahead option. You can prepare the caramelized onions a day in advance and store them in an airtight container in the refrigerator. When you're ready, simply reheat them gently before mixing with the egg and cream filling. The tart itself can also be baked a day ahead; it stores well in the refrigerator for up to three days—just reheating it in the oven for about 10-15 minutes at 350°F (175°C) to regain that fresh-baked warmth.

If you're thinking of making this tart for a larger event, it also freezes beautifully! After baking, let the tart cool completely, then wrap it tightly in plastic wrap followed by aluminum foil. You can freeze it for up to three months. To enjoy, simply thaw it overnight in the refrigerator and reheat in the oven to restore its crispiness. The flavors will meld beautifully during storage, making it a delightful option for planned gatherings.

Questions About Recipes

→ Can I use different types of onions?

Absolutely! While yellow onions are traditional, red or sweet onions can add unique flavors.

→ How do I store leftovers?

Store in an airtight container in the fridge for up to 3 days. Reheat in the oven for the best texture.

→ Can I make this tart ahead of time?

Yes, you can prepare the tart and store it in the fridge before baking. Just bake it when you're ready to serve.

→ What can I serve with this tart?

A light salad with vinaigrette pairs wonderfully, balancing the tart's rich flavors.