Walnut Creme Plum Tart

From chocolateandzucchini.com.

Ingedients

For the pâte sablée:

• 75 grams (⅓ cup plus 1 tablespoon) sugar (I use unrefined cane sugar, but regular white sugar is fine)
• 150 grams flour — if you use American all-purpose flour, use 1 cup plus 2 tablespoons
• 75 grams cold butter (I use salted, but you can use unsalted and add a pinch of salt) — if you use regular American butter (which has less butterfat than European butter), use 7 tablespoons
• Ice-cold water or milk

For the filling:

• 135 grams (1 ¼ cups) shelled walnut halves
• 2 tablespoons/40g sugar (I use unrefined cane sugar; regular white sugar is fine, honey would be lovely, too)
• 1 egg
• 3 tablespoons crème fraîche (substitute sour cream)
• Optional flavoring: 1 teaspoon pure vanilla extract, or 1 teaspoon plum or walnut liqueur, or 1 teaspoon dark rum
• 550 grams (1 ¼ pounds) ripe quetsche plums (substitute any other variety of plum)

Directions

Preheat the oven to 180°C (350°F). Grease a 10-inch tart pan with butter and set aside.

Prepare the pâte sablée. In the bowl of a mixer or blender, combine the sugar and flour. Add the butter and process in short pulses until the mixture resembles coarse meal. (Alternatively, rub the butter into the dry ingredients by hand with the tips of your fingers or a wire pastry blender.) Add a tablespoon of water or milk and mix again, in short pulses, until it is absorbed. The dough should still be crumbly, but it should clump if you gently squeeze a handful in your hand. If it doesn’t, add a little more water — teaspoon by teaspoon — and give the dough a few more pulses until it reaches the desired consistency.

Pour the mixture evenly into the prepared tart pan. Using the heels of your hands and your fingers, press on the dough gently to form a thin layer, covering the surface of the pan and creating a rim all around. Don’t worry if the dough feels a little dry, this is normal. (You can prepare the dough up to a day ahead: cover with plastic wrap and refrigerate.) Bake for 15 minutes, until lightly golden.

While the crust par-bakes, prepare the filling. Combine the walnuts and sugar in the bowl of your mixer, and grind to a coarse powder. Add the egg, crème fraîche, and flavoring if using, and mix again. (You can prepare the walnut cream up to a day ahead: transfer to an airtight container, refrigerate, and bring to room temperature before using.) Rinse and dry the plums, cut them in halves, and discard the stones.

Remove the pan from the oven (leave the heat on), and let cool slightly. Spread walnut cream evenly over the tart shell, and arrange the plums on top in a circular pattern starting from the outside. Return to the oven for 30 minutes, until the plums are cooked through and the walnut cream is set. Transfer to a rack to cool completely before serving. The tart is best served on the day it is made, but the leftovers will keep until the next day; cover with foil, refrigerate, and bring to room temperature before eating.