To prepare the crust, start by preheating your oven to 350°F (175°C). In a sizable mixing bowl, combine the flour, granulated sugar, and kosher salt. Pour in the melted butter and almond extract, stirring until a dough forms. Firmly press the dough into a 10-inch tart pan with a removable bottom, ensuring it covers the base and sides evenly.

Use a fork to prick the dough all over, then bake for 20-25 minutes, or until the crust turns a golden brown. Allow it to cool completely.

For the filling, use a hand mixer to whip the heavy cream in a medium bowl until stiff peaks form. In a separate large bowl, beat together the mascarpone and softened cream cheese until smooth. Incorporate the powdered sugar, lemon juice, and almond extract, mixing until the mixture is lump-free. Gently fold in the whipped cream until fully integrated.

Spread the creamy filling evenly over the cooled crust. Arrange the sliced strawberries, blackberries, raspberries, mandarins, and blueberries decoratively on top.

In a small, microwave-safe bowl, heat the apricot preserves with 2 teaspoons of water for about 30 seconds, or until warmed. Brush this mixture over the tart to give it a glossy finish. Refrigerate the tart for at least 2 hours before serving to ensure it is thoroughly chilled.