Caramelized Onion and Gruyère Tart

Ever had a dish that makes time stand still? This Caramelized Onion and Gruyère Tart is that showstopper. The moment those deeply caramelized onions hit your tongue, mingling with nutty, melted Gruyère and that buttery cornmeal crust… you’ll wonder how something so simple can taste so extraordinary.

What makes this tart magical is the patience behind it. Those onions aren’t just cooked—they’re transformed through a slow dance with butter and time, developing complex sweetness that’s then enhanced with a splash of Marsala. The cornmeal in the crust adds a subtle texture that perfectly complements the silky onion filling, while the Gruyère brings its signature nutty depth that no other cheese quite matches.

Ingredients

For the Buttery Cornmeal Pastry:

• 1 cup all-purpose flour
• 1/4 cup plus 2 tablespoons fine white cornmeal
• 1/2 teaspoon salt
• 1 stick (4 ounces) cold unsalted butter, cut into 1/2-inch cubes
• 1/4 cup ice water

For the Caramelized Onion Filling:

• 1 tablespoon unsalted butter
• 1 tablespoon vegetable oil
• 2 large onions, halved and thinly sliced
• 1/4 cup dry Marsala
• Kosher salt, to taste
• Freshly ground white pepper, to taste
• 6 ounces (1 1/2 cups) Gruyère cheese, coarsely shredded

Steps

Make the Cornmeal Crust:

1. In a food processor, pulse together the 1 cup flour, 1/4 cup plus 2 tablespoons cornmeal, and 1/2 teaspoon salt until combined. This quick mixing prevents overworking the dry ingredients.
2. Add the 4 ounces cold cubed butter and pulse 8-10 times until the mixture resembles small peas. You should still see visible butter pieces—these create flaky layers when baked.
3. Sprinkle 1/4 cup ice water over the mixture and pulse 3-4 times just until the pastry is evenly moistened. Stop immediately when the dough begins to clump—overmixing develops gluten and makes tough pastry.
4. Transfer the mixture to a lightly floured board and gently pat into a 5-inch disk without kneading. The dough should look somewhat shaggy but hold together when pressed.
5. Wrap the disk tightly in plastic wrap and refrigerate for at least 30 minutes or up to overnight. This crucial resting period allows the flour to hydrate and the butter to firm up, ensuring a flaky texture.

Prepare the Caramelized Onions:

6. In a large skillet over medium heat, melt 1 tablespoon butter with 1 tablespoon vegetable oil. The combination prevents the butter from burning during the long cooking process.
7. Add the sliced onions, cover, and cook over moderate heat for about 12 minutes, stirring occasionally, until softened but not browned. The cover helps the onions release moisture and begin softening.
8. Uncover the skillet and continue cooking for about 45 minutes, stirring every 5-7 minutes, until the onions are very soft and deep golden brown. If the onions start sticking, add 1-2 tablespoons water as needed and scrape up the flavorful browned bits. Patience is key—rushing this step will rob you of the deep caramelized flavor.
9. Pour in the 1/4 cup Marsala and stir constantly until nearly evaporated, about 2-3 minutes. The wine adds complexity and deglazes the pan, incorporating all the flavorful bits.
10. Season with kosher salt and white pepper to taste (start with 1/4 teaspoon of each). Transfer to a medium bowl and let cool slightly. White pepper keeps the filling visually clean without black specks.

Prepare and Blind Bake the Tart Shell:

11. Preheat the oven to 375°F (190°C). Position a rack in the center of the oven for even heat distribution.
12. On a lightly floured work surface, roll out the chilled pastry to a 13-inch round, approximately 1/8-inch thick. Work quickly to keep the butter cold—this ensures a flaky crust.
13. Carefully wrap the dough around your rolling pin and unroll it over a 10-inch fluted tart pan with a removable bottom. This technique prevents stretching or tearing the dough.
14. Gently press the dough into the corners without stretching it. Run the rolling pin over the rim to trim the overhang cleanly.
15. Using a fork, prick the bottom of the shell at 1/2-inch intervals (called “docking”) to prevent the dough from puffing up during baking.
16. Refrigerate the prepared shell for at least 10 minutes to relax the gluten and re-chill the butter.
17. Line the chilled tart shell with foil, pressing it gently against the sides, and fill with pie weights or dried beans. This prevents the bottom from puffing and the sides from shrinking.
18. Bake in the center of the oven for about 25 minutes, or until the edge turns golden and the center appears nearly set. The partially baked crust should look dry but not fully browned.
19. Remove the foil and weights carefully (they’ll be hot!), then cover just the edge with strips of foil to prevent over-browning. Return to the oven for 5 minutes longer, until the shell is fully cooked and golden throughout.

Assemble and Finish the Tart:

20. Sprinkle the 1 1/2 cups shredded Gruyère evenly into the hot tart shell. Adding cheese first creates a moisture barrier that helps keep the crust crisp.
21. Spread the caramelized onions evenly over the cheese layer. The residual heat from the shell will begin melting the cheese.
22. Bake for 10 minutes, or until the cheese is completely melted and the onions are sizzling. Look for bubbling around the edges and a slight browning on top.
23. Remove from oven and let cool for exactly 15 minutes on a wire rack. This resting period allows the filling to set slightly while keeping it warm for serving.
24. Carefully remove the outer ring of the tart pan by placing the tart on a wide can or bowl and allowing the ring to fall away. Slide the tart from the metal base onto a serving platter.
25. Cut into wedges and serve warm. For the cleanest cuts, use a sharp knife wiped clean between slices.

Smart Swaps

• Replace Gruyère with aged Gouda or Comté (1:1 ratio) for a different but equally delicious flavor profile
• Substitute dry sherry for the Marsala if needed (same amount)
• Use gluten-free flour blend plus 1/4 teaspoon xanthan gum instead of all-purpose flour for a gluten-free version
• Try 2 tablespoons fresh thyme leaves added to the onions for an herbal note

Make It Diabetes-Friendly

• Use a whole grain pastry flour instead of all-purpose (reduces net carbs by approximately 5g per serving)
• Reduce cornmeal to 3 tablespoons and replace remaining amount with almond flour (lowers glycemic impact)
• Serve smaller portions (1/10 of tart instead of 1/8) alongside a protein-rich side to slow carbohydrate absorption
• Add 1/2 cup chopped walnuts to the filling for healthy fats that reduce glycemic response

Pro Tips

• For the ultimate caramelized onions, use sweet onions like Vidalia or Walla Walla
• Chill your food processor blade for 15 minutes before making the dough for the flakiest results
• The tart reheats beautifully at 325°F (165°C) for 10 minutes – perfect for make-ahead entertaining
• For a picture-perfect presentation, brush the exposed crust edge with egg wash (1 beaten egg with 1 tablespoon water) before the final bake