Prepare Tartlet Shells: In a food processor, combine plain flour, icing sugar, and salt until well blended. Add cold unsalted butter, pulsing until it resembles coarse crumbs. Crack in an egg, mixing briefly until a dough forms. Wrap in plastic wrap and chill in the refrigerator for at least 1 hour.

Shape and Bake Shells: Preheat oven to 160°C (325°F). Roll out chilled dough to about 3mm thick. Cut into rounds for a greased muffin pan, pressing gently. Chill for 15 mins, then add parchment and weights. Bake for 15 mins, remove weights, and bake for more 5-8 mins until golden brown.

Make Orange Curd: In a saucepan, whisk together orange juice, zest, egg yolks, caster sugar, and cornstarch. Cook over low heat, stirring constantly until it thickens and coats the back of a spoon, about 10 mins. Stir in butter until melted. Strain into cooled tartlet shells and refrigerate for at least 2 hours.

Prepare Ganache: Chop chocolate and place in a mixing bowl. Heat cream until simmering, pour over chocolate, and let sit. Stir until smooth. Let cool slightly before piping over chilled orange curd.

Decorate and Serve: Optionally decorate with dehydrated orange slices or extra zest. Allow tartlets to sit at room temperature for 10-15 mins before serving.