Instructions

For the Hazelnut Tart Dough

• In the work bowl of a food processor, pulse together the hazelnuts and confectioners’ sugar until combined.
• Add the flour, salt, cinnamon and nutmeg and pulse until combined. Add the cold butter, and pulse until mixture is crumbly.
• In a small bowl, whisk together egg and 1 tablespoon water. Pour the egg mixture over the surface of the flour-hazelnut mixture in the food processor. Pulse until the dough just starts to come together but is still a little crumbly.
• Reserve 1 cup (235 grams) of the hazelnut mixture for the topping. Place it in a bowl or wrap it in plastic and refrigerate until ready to use.
• Pour the rest of the hazelnut mixture into a 9-inch springform pan. Place about 2 tablespoons of flour on a piece of wax paper. Pat your fingers in the flour and then press the hazelnut dough into the bottom and up the sides of the pan.
• The springform pan I used is 3 1/4-inches high. Press the dough 2-inches up the side of the pan. It should be about 1/4-inch thick.
• Freeze the tart shell until firm, about 1 hour. This tart shell can sit in the freezer overnight. Place the 1 cup of reserved hazelnut mixture in the refrigerator.

For the Plum Filling

• Preheat oven to 375°F (190°C).
• In a small bowl, combine granulated sugar and vanilla bean seeds and rub together with your fingertips. Stir in the salt and the cornstarch; set aside.
• Roughly chop 1/4 cup of hazelnuts and set aside.
• Cut smaller plums into quarters and larger plums into 6 pieces. Starting from the outside edge, arrange the plums on their side, in tight concentric circles. They should be tightly packed. Sprinkle the plums with the sugar-cornstarch mixture. Crumble the reserved hazelnut mixture over the plums. Sprinkle with chopped hazelnuts.
• Place the pan on a rimmed baking tray (in case of leakage). Bake until the hazelnut topping is a deep golden brown and fruit is bubbly, 50 to 60 minutes. Cover the pan with foil to prevent excess browning, if necessary.
• Remove the tart from the oven and let it cool completely in the pan. Remove the ring and serve at room temperature with ice cream or whipped cream.