- For the pastry crust, beat the butter and icing sugar with electric beaters or a stand mixer fitted with the paddle attachment on medium-high speed, or by hand, until fluffy. Beat in the egg yolks, vanilla and almond extracts until well combined.
- Sift in the flour, cardamom and salt. Blend on low speed (or by hand) until evenly combined. Shape the dough into 2 discs, wrap in plastic wrap and chill until firm, at least 2 hours.
- Have ready a 12 × 4-inch (30 × 10 cm) rectangular fluted pan with a removable bottom. You can pull the chilled dough from the fridge 30 minutes before rolling.
- On a lightly floured surface, roll out the dough to a rectangle about 1/4 inch (0.5 cm) thick. Line the tart pan with the dough, pressing it in and trimming away the excess. Dock the pastry with a fork (to prevent air bubbles) and chill, uncovered, for 30 minutes.
- Preheat the oven to 325°F (160°C). Place the chilled tart shell on a baking tray and bake for about 20 minutes, until lightly browned at the edges. Let cool completely on a wire rack before filling.
- To make the filling, beat the mascarpone by hand to soften it a little and then stir in the sour cream (or yogurt), icing sugar, orange zest, vanilla and brandy (or orange liqueur). Spoon into the cooled tart shell, spread evenly and level the top.
- Use a serrated knife to trim the top and bottom from each orange and the grapefruit, and then cut away and discard the rest of the peel, including the white pith. Using a paring knife, gently segment the fruit and separate the flesh from the white membrane. Try to keep each segment whole. Place the flesh in a bowl and discard the membranes. Arrange the citrus segments over the mascarpone filling, alternating colours.
- Heat the apple jelly (or apricot jam) in a small saucepan over medium-high heat, stirring until melted. Use a pastry brush to brush the citrus segments with the melted jam (to seal them and add shine). Sprinkle with the chopped pistachios and chill, uncovered, for at least an hour before serving.
Recipe adapted from Set for the Holidays with Anna Olson, Appetite for Random House, 2018