1. To make the pastry, in a food processor, combine the flour, confectioners’ sugar, and salt and process briefly to mix. Add the butter and process until the mixture is the consistency of coarse meal, 5 to 10 seconds.

2. With the motor running, add the egg yolk and then gradually the ice water. Process until the dough just begins to come together and will hold a shape when pressed.

3. Transfer the dough to a floured work surface and press into a thick disk for easy rolling. Roll out into a round at least 1½ inches in diameter and about ¼ inch thick. Drape the dough round over the rolling pin, position it over a 10-inch tart pan with a removable bottom, and ease it into the bottom and sides of the pan, pressing the pastry gently into place. If using a pan with fluted sides, roll the rolling pin over the top edge of the pan with moderate pressure to trim away the excess dough. If using a pan with straight sides, raise the edges of the pastry ¼ to ½ inch above the rim of the pan by squeezing the dough from both sides with your index fingers. Place the tart pan on a baking sheet.

4. Preheat the oven to 400°F

5. To make the filling, in a food processor, finely grind the hazelnuts. Add the granulated sugar, butter, flour, and hazelnut liqueur. Pulse until a meal-like paste forms. Add the eggs and process for 10 seconds to incorporate. Spread the mixture in an even layer in the pastry-lined pan.

6. To make the topping, arrange the plum slices in overlapping concentric circles on the filling. Be sure to fit them tightly together. Arrange 2 concentric rows of the plum slices in the center of the tart.

7. Dot the plums with the butter and dust with the granulated sugar. Bake until the tart is browned on top, about 1 hour. Transfer to a rack and let cool completely

8. Garnish the tart with the hazelnuts and serve.