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Creamy Vidalia Sweet Onion Tart Recipe Easy Homemade Gruyère Custard with Thyme

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A savory tart featuring sweet Vidalia onions caramelized to perfection, combined with a silky Gruyère custard and fresh thyme, perfect for brunch or a light dinner.

Ingredients

Scale
  • 1 ¼ cups (160g) all-purpose flour
  • ½ tsp salt
  • ½ cup (113g) unsalted butter, cold and cubed
  • 3–4 tbsp ice water
  • 4 large Vidalia sweet onions, thinly sliced
  • 2 tbsp unsalted butter
  • 1 tbsp olive oil
  • 1 tsp fresh thyme leaves, plus extra for garnish
  • 1 cup (240ml) heavy cream
  • 3 large eggs, room temperature
  • 1 cup (100g) grated Gruyère cheese
  • Salt and freshly ground black pepper to taste

Instructions

  1. Make the Tart Crust (15 minutes plus chilling): In a food processor, pulse the flour and salt. Add cold butter cubes and pulse until the mixture resembles coarse crumbs with some pea-sized pieces. Slowly add ice water, one tablespoon at a time, pulsing until the dough just comes together. Don’t overwork it! Wrap in plastic and chill for at least 30 minutes.
  2. Caramelize the Onions (20 minutes): While the dough chills, heat butter and olive oil in a large skillet over medium-low heat. Add the sliced Vidalia onions and thyme leaves, seasoning lightly with salt. Stir occasionally, letting the onions soften and turn golden brown without burning. This slow caramelization is key for that sweet depth. If they start browning too fast, lower the heat.
  3. Preheat Oven and Prepare Crust (10 minutes): Set your oven to 375°F (190°C). Roll out the chilled dough on a floured surface to about 12 inches (30 cm) diameter. Gently place it in the tart pan, pressing into edges and trimming excess. Use a fork to prick the bottom to prevent puffing. Chill again for 10 minutes if the dough feels warm.
  4. Blind Bake the Crust (15 minutes): Line crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then remove weights and bake an additional 5 minutes until the crust is lightly golden. This prevents sogginess from the custard.
  5. Prepare the Gruyère Custard (5 minutes): In a bowl, whisk together eggs, heavy cream, grated Gruyère, salt, and pepper until smooth. Set aside.
  6. Assemble and Bake (30 minutes): Spread the caramelized onions evenly over the crust. Pour the custard mixture on top, slowly to avoid displacing the onions. Bake at 375°F (190°C) for about 30 minutes, or until the custard is set but still slightly jiggly in the center. It will firm up as it cools.
  7. Cool and Garnish: Let the tart cool for at least 15 minutes before removing from the pan. Garnish with fresh thyme sprigs.

Notes

Caramelize onions slowly over low heat to avoid bitterness. Blind bake the crust to prevent sogginess. Beat eggs and cream gently to avoid air bubbles in custard. Use pie weights or dried beans for blind baking. Tent with foil if edges brown too quickly. Cool tart before slicing for clean cuts.

Nutrition

Keywords: Vidalia onion tart, Gruyère custard, savory tart, caramelized onions, thyme, brunch recipe, easy tart recipe, homemade tart

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