Classic Flamiche aux Poireaux with Gruyère

Why You’ll Love This Recipe

• Classic French comfort: silky leeks, delicate custard, and a buttery, flaky crust.
• Approachable technique with make-ahead options for stress-free entertaining.
• Balances richness with gentle sweetness from slow-sweated leeks.
• Light blanket of Gruyère adds nutty depth without overpowering the leeks.

Grocery List

• Produce: 4 large leeks
• Dairy: Unsalted butter, crème fraîche, whole milk, Gruyère cheese, 1 large egg yolk, 3 large eggs
• Pantry: All-purpose flour, fine sea salt, white pepper, ground nutmeg, optional dry white wine

Full Ingredients

Buttery Tart Shell (Pâte Brisée)

• 250 g all-purpose flour (about 2 cups)
• 150 g cold unsalted butter, cut into 1/2-inch cubes (10 1/2 tbsp)
• 1/2 tsp fine sea salt
• 1 large egg yolk
• 2–4 tbsp ice water (30–60 ml), as needed

Leek Filling & Custard

• 4 large leeks, white and light green parts only, halved lengthwise and thinly sliced (about 700 g before trimming)
• 45 g unsalted butter (3 tbsp)
• 3/4 tsp fine sea salt, divided
• 1/4 tsp ground white pepper
• Pinch freshly grated nutmeg (about 1/8 tsp)
• Optional: 60 ml dry white wine (1/4 cup) or water
• 200 ml crème fraîche (about 3/4 cup + 1 tbsp)
• 60 ml whole milk (1/4 cup)
• 3 large eggs
• 85 g Gruyère, finely grated (3 oz; about 1 cup loosely packed)

Step-by-Step Instructions

Step 1: Make the pâte brisée

In a large bowl, whisk the flour and salt. Toss in the cold butter. Using fingertips or a pastry cutter, cut the butter into the flour until pea-sized bits remain with some larger flat shards for flakiness. Mix in the egg yolk. Sprinkle in 2 tbsp ice water and gently toss; add more water 1 tbsp at a time just until the dough holds together when pressed. Turn out, gather into a disk, wrap, and chill 45 minutes.

Step 2: Roll, line, and chill the tart shell

On a lightly floured surface, roll the dough to a 12-inch (30 cm) circle. Ease it into a 9-inch (23 cm) tart pan with a removable bottom, pressing gently into the corners. Trim excess to a 1/2-inch overhang, fold in for a thicker rim, and press. Dock the base with a fork and freeze 15 minutes to minimize shrinkage.

Step 3: Blind-bake the shell

Heat the oven to 375°F (190°C) with a rack in the center. Line the chilled shell with parchment and fill with pie weights or dried beans. Bake 18 minutes. Carefully remove parchment and weights, then bake 7–10 minutes more until the crust is set and pale golden. Cool slightly. Reduce oven temperature to 350°F (180°C).

Step 4: Sweat the leeks gently

While the shell bakes, clean the leeks thoroughly by rinsing between layers. In a large skillet over low heat, melt the butter. Add the leeks and 1/2 tsp salt. Cover and cook, stirring occasionally, for 15 minutes until very soft but not browned. Uncover, add white wine if using, and cook until the liquid evaporates and the leeks are sweet and jammy, 5–8 minutes more. Season with white pepper and nutmeg. Let cool 10 minutes until warm, not hot.

Step 5: Whisk the custard

In a bowl, whisk the eggs, crème fraîche, milk, and remaining 1/4 tsp salt until smooth. Fold the warm leeks into the custard. Taste and adjust seasoning, keeping in mind the Gruyère adds salt.

Step 6: Assemble and bake

Place the tart shell on a rimmed baking sheet. Pour in the leek-custard mixture and smooth the surface. Sprinkle evenly with the Gruyère. Bake at 350°F (180°C) for 25–30 minutes until the edges are puffed, the center has a slight jiggle, and the top is lightly golden. If you have an instant-read thermometer, the center should read about 165°F (74°C).

Step 7: Rest, unmold, and serve

Cool on a rack for 15–20 minutes to set. Carefully remove the tart ring. Slice with a serrated knife. Serve warm or at room temperature, ideally with a simply dressed green salad.

Pro Tips

• Keep everything cold for the crust: cold butter, minimal handling, and a quick freeze before blind-baking prevent shrinkage and toughening.
• Low and slow for leeks: gentle heat keeps them pale and sweet; browning can add bitterness.
• Let the leeks cool to warm before mixing with eggs to avoid curdling the custard.
• Grate Gruyère finely so it melts into a delicate, even blanket instead of heavy patches.
• Bake on a preheated baking sheet for extra insurance against a soggy bottom.

Variations

• Picardy-style pastry: Use all-butter puff pastry or a simple yeasted dough in place of pâte brisée for a regional twist.
• Smoky bacon: Add 75 g (2.5 oz) crisped lardons to the leeks for a heartier version.
• Cheese swap: Try Comté or Emmental in place of Gruyère; add a teaspoon of chopped thyme for an herbal note.

Storage & Make-Ahead

The dough can be made up to 2 days ahead or frozen for 2 months. Blind-bake the shell up to 1 day ahead and keep loosely covered at room temperature. The leek mixture can be cooked 2 days ahead and refrigerated. Leftover tart keeps 3 days in the refrigerator; reheat slices at 300°F (150°C) for 12–15 minutes, or enjoy at room temperature. For freezing, wrap slices tightly and freeze up to 1 month; reheat from frozen at 325°F (165°C) for 20–25 minutes.

Nutrition (per serving)

Approximate values: 470 calories; 34 g fat; 28 g carbohydrates; 13 g protein; 2 g fiber; 420 mg sodium.