Lightly grease a 9-inch tart pan with a removable base with nonstick spray.

In a food processor, combine the flour, confectioners’ sugar, and salt and pulse or process on low speed to combine. Add the butter, 1 Tablespoon at a time, pulsing a few times after each addition. Add the egg and pulse only until the dough comes together in a clump. The dough should be soft. Transfer it to a lightly floured surface and press it into a 1-inch-thick disc. *If you don’t have a food processor, use a handheld or stand mixer fitted with a paddle attachment. Beat the dry ingredients together, and then beat in the butter on medium speed 1 Tablespoon at a time, and then beat in the egg.*

Place the soft dough in the prepared pan and use your hands to press it evenly into the pan and up the sides. It may seem like you don’t have enough dough at first, but keep pressing. Use the bottom of a metal measuring cup to press the edges firmly against the rim of the pan. Flatten the top edge so it’s even with the rim of the pan, or use a paring knife to trim. Save the scraps to patch up any thin-looking areas. Prick the bottom of the crust all over with a fork. Cover and freeze for at least 30 minutes or up to 1 day.

Preheat the oven to 350°F (177°C). Remove the crust from the freezer and place the tart pan on a large baking sheet for easy handling.

Bake for 25 minutes or until the crust appears set. Place on a cooling rack to cool completely.

Using a handheld or stand mixer fitted with a whisk attachment, beat the heavy cream, 6 Tbsp (45g) confectioners’ sugar, the lemon zest, vanilla extract, and vanilla bean seeds until stiff peaks form, about 3–4 minutes. In a small bowl using a fork, gently mix the mascarpone with the remaining confectioners’ sugar. Don’t over-mix; you only want to smooth out the mascarpone here. Over-mixing will result in a separated mixture.

Transfer the mascarpone mixture to the whipped cream mixture. Fold together with a silicone spatula or beat on low speed until combined. Use right away (next step), or cover and refrigerate the filling for up to 3 days before using.

Spread the filling into the cooled crust. I usually use a small offset spatula for this. Refrigerate until ready to garnish with fruit, or garnish right away.

Garnish the tart with fresh fruit. Use a fork to whisk together the jam and water in a small microwave-safe bowl. Warm for about 15 seconds in the microwave, then brush the glaze on top of the fruit.

Slice and enjoy! Store leftover fruit tart, covered, in the refrigerator for up to 3 days.