Parisian Custard Tart

Directions

1. Custard Tart
2. To make the filling: Give a medium heavy-bottomed saucepan a quick rinse with cold water, but don’t dry the pan (this will help prevent the milk from scorching), then pour in the milk and water. Stir in half of the granulated sugar and bring just to a boil—keep an eye on it: Once the milk boils, it’s just a nanosecond before it bubbles over the pot and makes a mess. Remove the pan from the heat.
3. While the liquids are heating, whisk together the rest of the granulated sugar, the brown sugar and cornstarch in a large bowl. Add the eggs and whisk energetically to blend well. Put the bowl on a folded kitchen towel or a silicone pot holder to anchor it. Whisking the sugar-egg mixture nonstop, drizzle in about one quarter of the hot liquid. Then, still whisking, pour in the rest in a steadier stream.
4. Rinse the saucepan (no need to be thorough) and pour the custard mixture into it. Set the pan over medium heat and, whisking without stopping and making sure that the whisk reaches every part of the pan, including the corners, cook the custard until the first bubble rises to the top and pops, at which point the custard will be noticeably thicker and your whisk will leave tracks. Lower the heat a bit and cook and stir for another minute or two, your insurance that the custard is sufficiently cooked and that the cornstarch won’t taste raw.
5. Scrape the custard into a clean bowl and stir in the rum, if you’re using it, and vanilla. Press a piece of plastic wrap against the surface and let the custard sit at room temperature for about 30 minutes; stir now and then if you’re around.
6. Put the bowl in the refrigerator and chill the custard for at least 1 hour. Better yet, let it get thoroughly cold. You can speed the process by placing the custard bowl in a larger bowl filled with ice cubes and cold water—come back to the bowl now and then to stir until it’s cold. (The custard can be refrigerated in an airtight container overnight.)
7. To make the crust: Butter a 9-inch springform pan (if your pan is 9½ inches, that’s fine).
8. If you’re using puff pastry, roll it out into a round that’s 12 to 13 inches in diameter (see headnote); if you’re using tart dough, you’re all set. Using your hands or rolling the pastry up around your pin to make it easier, position the pastry over the pan. Gently ease it into the pan and press it against the bottom and up the sides. You’re aiming for the dough to come about 1½ inches up the sides. If the edges are ragged and uneven, just leave them—they’ll get trimmed later. Put the pan in the refrigerator until ready to use; when the crust is firm, cover it tightly.
9. When you're ready to bake, preheat the oven to 425°F.
10. Remove the custard from the fridge and whisk it a bit to loosen it, then scrape it into the pastry-lined springform pan and smooth the top. Using a table knife, trim the dough so that it reaches just about ½ inch above the custard.
11. Bake the tart for 50 to 55 minutes, or until the top of the custard is dark, dark brown—if it looks black in places, that’s great and most authentic. It won’t be brown all over, though, and it might bubble and mound in places. If you get bubbles, you can prick them with the tip of a knife or just leave them.
12. Transfer the pan to a rack and wait for 5 minutes, then, if some of the custard has risen above the crust and stuck to the sides of the pan, run a table knife gently between the pan and the custard. Let the flan cool to room temperature, then cover it lightly and refrigerate it. It’s best if you can chill it overnight, but that’s not always convenient—give it as much time as you can.
13. When you’re ready to serve, remove the sides of the springform and if you’d like, lift the tart off the base and onto a serving platter (if it’s easier, leave it on the base). You can serve it cold, at room temperature or at any temp in between. Cut into wedges and serve with a fork...or don’t. When you’re having the tart as a snack, do as Parisians do: Eat it out of hand.
14. Covered tightly, the tart will keep for about 3 days in the fridge. Make sure to keep it away from foods with strong odors.

1. All-Purpose Tart Dough
2. Put the flour, sugar and salt in a food processor and pulse to blend. Scatter over the pieces of butter. You want to cut the butter into the dry ingredients until you’ve got some pieces the size of oatmeal flakes and others the size of peas. Work in long pulses—you might need as many as 20—and scrape the bowl often. Stir the egg and water together and add in 3 additions, pulsing after each. Then pulse until the dough just starts to come together, forms moist curds and clumps and holds together when pinched.
3. Turn the dough out onto a work surface, knead into a compact ball and flatten into a disk, then sandwich between sheets of parchment. Roll the dough into an 11-inch round. If it’s cold enough, fit it into a 9- to 9½-inch fluted tart pan with a removable bottom or into a pie pan, prick the bottom with a fork and trim the top even with the pan’s rim. If it’s not cold, chill it until it’s workable and then proceed. Refrigerate the crust in the pan for at least 1 hour.