Also, this video has spent a long-time in the editing room (also known as the Rules house in HP), and I'm pretty sure our friends forgot about it and how adorable they look dancing to "Zou Bisou Bisou". Thanks friends, for busting out the dance moves, your French phrases and hearty appetites.
Also, also, this was a fun one to shoot, so... enjoy.
Mustard Tart via bonappetempt.com and originally via Around My French Table
For dough (Makes one 9- to 9 1/2-inch tart shell)
Note: The dough should chill for at least 3 hours.
1 1/4 cups all-purpose flour
1 teaspoon sugar
1/2 teaspoon salt
6 tablespoons (3/4 stick) very cold (or frozen) unsalted butter, cut into bits
1 large egg
3 thin carrots, trimmed and peeled
3 thin leeks, white and light green parts only, cut lengthwise in half and washed
2 rosemary sprigs
3 large eggs
6 tablespoons creme fraiche or heavy cream
2 tablespoons Dijon mustard, or to taste
2 tablespoons grainy mustard, preferably French, or to taste
Salt, preferably fleur de sel, and freshly ground white pepper
1 9- to 91/2-inch tart shell made from Tart Dough, partially baked and cooled
ice water, as needed
To make the dough in a food processor: Put the flour, sugar, and salt in the processor and whir a few times to blend. Scatter the bits of butter over the flour and pulse several times, until the butter is coarsely mixed into the flour. Beat the egg with the ice water (I used a couple of tablespoons) and pour it into the bowl in 3 small additions, whirring after each one. (Don't overdo it -- the dough shouldn't form a ball or ride on the blade.) You'll have a moist, malleable dough that will hold together when pinched. Turn the dough out onto a work surface, gather it into a ball (if the dough doesn't come together easily, push it, a few spoonfuls at a time, under the heel of your hand or knead it lightly), and flatten it into a disk.
To make the dough by hand: Put the flour, sugar, and salt in a large bowl. Drop in the bits of butter and, using your hands or a pastry blender, work the butter into the flour until it is evenly distributed. You'll have large and small butter bits, and that's fine -- uniformity isn't a virtue here. Beat the egg and water together, drizzle over the dough, and, using a fork, toss the dough until it is evenly moistened. Reach into the bowl and, using your fingertips, mix and knead the dough until it comes together. Turn it out onto a work surface, gather it into a ball (if the dough doesn't come together easily, push it, a few spoonfuls at a time, under the heel of your hand or knead it some more), and flatten it into a disk.
Chill the dough for at least 3 hours. (The dough can be refrigerated for up to 5 days.)
When you're ready to make the tart shell, butter a 9- to 9 1/2-inch fluted tart pan (I used a regular springform pan) with a removable bottom (butter it even if it's nonstick).
Roll out the dough, making sure to lift and turn the dough and reflour the counter often. The rolled-out dough should be about 1/4 inch thick and at least 12 inches in diameter.
Transfer the dough to the tart pan, easing it into the pan without stretching it. (What you stretch now will shrink in the oven later.) Press the dough against the bottom and up the sides of the pan. If you'd like to reinforce the sides of the crust, you can fold some of the excess dough over, so that you have a double thickness around the sides. Using the back of a table knife, trim the dough even with the top of the pan. Prick the base of the crust in several places with a fork.
Chill or freeze the dough for at least 1 hour before baking.
Center a rack in the oven and preheat the oven to 400 degrees F. Press a piece of buttered foil (or use nonstick foil) against the crust's surface. If you'd like, you can fill the covered crust with rice or dried beans (Dorie says the beans will be inedible after this but I used lentils and then totally made a soup with them.) to keep the dough flat, but this isn't really necessary if the crust is well chilled. Line a baking sheet with a silicone baking mat or parchment paper and put the tart pan on the sheet.
To partially bake the crust: Bake for 20 minutes, then very carefully remove the foil (with the rice or beans). Return the crust to the oven and bake for another 3 to 5 minutes, or until it is lightly golden. Transfer the baking sheet to a cooling rack and allow the crust to cool before you fill it.
Center a rack in the oven and preheat the oven to 425 degrees F. Line a baking sheet with a silicone baking mat or parchment paper.
Cut the carrots and leeks into slender bâtons or sticks: First cut the carrots lengthwise in half, then place the halves cut side down on the cutting board and cut crosswise in half or cut into chunks about 3 inches long. Cut the pieces into 1/ 8- to 1/4-inch-thick matchsticks. If your carrots were fat and you think your matchsticks don't look svelte enough, cut them lengthwise in half. Cut the leeks in the same way.
Fit a steamer basket into a saucepan. Pour in enough water to come almost up to the steamer, cover, and bring to a boil. Drop the carrots, leeks, and 1 rosemary sprig into the basket, cover, and steam until the vegetables are tender enough to be pierced easily with the tip of a knife, 10 to 15 minutes. Drain the vegetables and pat them dry; discard the rosemary sprig.
In a medium bowl, whisk the eggs together with the creme fraîche or heavy cream. Add the mustards, season with salt and white pepper -- mustard has a tendency to be salty, so proceed accordingly -- and whisk to blend. Taste and see if you want to add a little more of one or the other mustards.
Put the tart pan on the lined baking sheet and pour the filling into the crust. Arrange the vegetables over the filling -- they can go in any which way, but they're attractive arranged in spokes coming out from the center of the tart. Top with the remaining rosemary sprig and give the vegetables a sprinkling of salt and a couple of turns of the pepper mill.
Bake the tart for about 30 minutes, or until it is uniformly puffed and lightly browned here and there and a knife inserted into the center of the custard comes out clean. Transfer the tart to a cooling rack and let it rest for 5 minutes before removing the sides of the pan.
Serve hot, warm, or at room temperature (or lightly chilled).