Flan Pâtissier (French Custard Tart)

Step 1: Put the milk, vanilla seeds, reserved vanilla beans and 50 g (1/4 cup) of the sugar in a large saucepan over medium-high heat. Bring it just to the point before boiling, stirring to dissolve the sugar. Remove from the heat, cover and leave to steep for 10 minutes.

Step 2: Meanwhile, put the egg yolks, whole egg and remaining sugar in a large bowl. Whisk to combine, then add the cornflour/cornstarch and whisk until smooth.

Step 3: While whisking the egg mixture, slowly pour in about half the milk in a thin stream. Whisk until combined.

Step 4: Pour the egg-and-milk mixture back into the saucepan and whisk to combine. Set over medium-low heat and stir constantly so the base does not catch. Continue until the custard starts to thicken; this should take 3–5 minutes. If it becomes lumpy, remove it from the heat and whisk vigorously until smooth.

Step 5: When the custard is thick and hot and the first large, slow bubbles appear on the base, whisk constantly on the stove for a further 20 seconds, then remove from the heat. Pause stirring briefly if needed to check for bubbles.

Step 6: Whisk in the butter until fully incorporated.

Step 7: Immediately strain the custard through a fine-mesh strainer into a bowl and discard the vanilla bean. Cover with cling wrap touching the custard's surface. Cool on the counter for 3 hours or more, then refrigerate for 12–24 hours.

Step 8: Keep the pastry as frozen as possible while working with it; it is easier to handle that way.

Step 9: Using the inside of the pan as a guide, cut a round base from one sheet of puff pastry. From the other sheet, cut three strips, each 25 x 5.5 cm (2.15 x 10 inches). Put the base and strips back in the freezer. Reserve the pastry offcuts for patching.

Step 10: Butter the sides of a 20 cm / 8-inch springform pan and line them with a 5.5 cm / 2.2-inch strip of baking paper. Do not use the pan base.

Step 11: Place the pan ring on a square of baking paper on a plate. Remove the cut pastry from the freezer. Working quickly, once the side strips have thawed just enough to bend, line the pan sides with pastry, overlapping the strips by 1 cm / 0.4 inch. Use water to seal the overlaps, pressing them down for now; they will be sealed properly later.

Step 12: Brush the base of the sides with water and fit the pastry base into the pan.

Step 13: Use the back of a teaspoon to press the base into the corner. Smear the thawing puff pastry to seal it fully.

Step 14: Prick the base 30 times with a fork.

Step 15: Cover with cling wrap and freeze for 4–24 hours.

Step 16: Preheat the oven to 220°C/430°F (200°C fan) for 30 minutes.

Step 17: Lift the crust using the baking paper and place it, still on the paper, on a tray. Crumple two 60 cm / 2-foot sheets of baking paper and arrange them in an X inside the crust. Fill with baking beads to 1 cm / 0.4 inch below the rim, pressing the paper into the corners.

Step 18: Bake for 25 minutes. Carefully lift out the baking beads using the overhanging paper. If the sides look as though they may cave in, return the crust to the oven with the beads for 5 minutes. Bake the crust for a further 5 minutes without the beads, then cool for 10 minutes. Seal any visible cracks with puff pastry scraps.

Step 19: Lower the oven temperature to 200°C/390°F (180°C fan).

Step 20: Remove the crème pâtissière from the refrigerator and whisk to loosen it. Scrape it into the crust, filling to 1 cm / 0.4 inch below the rim. Smooth the surface and gently brush it with all the whisked egg yolk.

Step 21: Bake for 65 minutes, rotating the tray 180 degrees after 45 minutes. The tart will puff up during the last 15 minutes. Remove it from the oven while it is still very wobbly; it will set as it cools. If the top is not golden, switch on the broiler to caramelize the surface, watching carefully because this takes only a few minutes.

Step 22: Cool on the counter in the pan for 4 hours. Transfer the tart, still in its pan, to a plate. Cover loosely with cling wrap and refrigerate for at least 12 hours.

Step 23: Remove from the refrigerator 1 hour before serving to bring the tart to room temperature. Cut into slices like a cake. The pastry is crisp and flaky, and the custard cuts neatly while remaining soft and creamy. In France, it is traditionally eaten as a handheld bakery treat; a plate works too.

Step 24: The pastry is at its crispest during the first 24 hours after the tart is refrigerated. It softens after that.