Place the plain flour, powdered sugar, almond flour, salt, orange zest (if using), and chilled unsalted butter into a food processor. Pulse until the mixture resembles fine breadcrumbs. Add the egg yolk and cold water, then pulse again until the dough starts to clump. Tip the mixture onto your work surface and gather it into a ball, kneading briefly until smooth. If the dough is too soft, wrap it in parchment and chill in the fridge for 15 minutes. Set the pastry aside for the next step.

Grease a 23cm/9in loose-bottomed tart tin. On a piece of parchment paper, trace a circle 4cm wider than the base of the tin. Dust the tin base with flour, place the pastry ball from Step 1 in the center, and flatten it slightly. Roll the pastry out, turning the paper as you go, until it reaches the marked circle. Gently lift the pastry and place it into the tin, pressing it into the corners and up the sides. Repair any cracks by pressing the dough together. Lightly prick the base of the pastry with a fork (not all the way through), then chill the assembled tin in the fridge for 30 minutes.

Preheat the oven to 200°C/180°C Fan/390°F/gas mark 6. Remove the pastry-lined tin from the fridge and line it with foil. Fill with baking beans to support the sides. Bake for 12-15 minutes, then carefully remove the foil and beans. Trim the excess pastry with a potato peeler to neaten the edges. Return the shell to the oven and bake for another 10-12 minutes, or until lightly golden and completely dry. Allow it to cool while preparing the filling. I always make sure my pastry is golden and crisp to prevent it from getting soggy once the filling is added.

[Optional] If using fresh oranges, zest them and set aside the zest for later, then juice the oranges. Heat the orange juice in a small pot over low heat until it simmers. Meanwhile, whisk together the eggs, superfine sugar, and cornstarch in a bowl until smooth. Once the juice simmers, slowly pour it over the egg mixture while whisking constantly to temper the eggs. Mix until smooth and return the mixture to the pot. Cook over low heat, stirring continuously, until it thickens. Remove from heat and transfer to a mixing bowl. Whisk in the powdered gelatin until dissolved. Let it cool slightly before adding the softened butter, reserved orange zest (if using), and Angostura orange bitters (if using). Whisk thoroughly to combine. For an extra zing, I sometimes add a touch more orange zest at this point!

Pour the orange filling from Step 4 into the cooled pastry case. Lightly drop the tart case on the countertop a few times to release any air bubbles. Refrigerate the tart for at least 3 hours, or overnight for the best result, until fully set.

Remove the tart from the tin. In a bowl, combine the heavy cream, powdered sugar, and Angostura orange bitters (if using). Whisk together until the cream forms firm peaks. I prefer to chill my bowl and whisk for a few minutes beforehand—this really helps the cream whip up quickly and hold its shape.

Decorate the set orange tart as desired with the whipped cream from Step 6, orange segments, crushed pistachios, and fresh mint leaves. Feel free to get creative—try piping the cream or scattering the pistachios and mint for an elegant finish! Serve chilled and enjoy.