Cook cranberries. Meanwhile, make the filling. In a saucepan set over medium heat, bring the cranberries, water, orange juice, cinnamon, cardamom, and ginger to a simmer. Turn the heat down to low and cook the mixture until the cranberries pop and have broken down, about 12-15 minutes.
Whisk eggs and sugar. Whilst the cranberries mixture cooks, in a separate bowl, combine the yolks and sugar and whisk until they are pale in colour, about 2 minutes, then set aside.
Extract the cranberry sauce. Pour the cranberry mixture into a fine-mesh sieve set over a bowl, pressing the pulp gently with a spoon to get as much puree out as possible. Be sure to scrape the underside of the strainer as well to get all the puree. Discard the pulp and spices and pour the strained puree back into the saucepan.
Add back into the saucepan and make the curd. Add the egg mixture and cook over medium heat, constantly whisking, until the consistency thickens enough to coat the back of a spoon, 5 to 7 minutes.
Finish curd, add to a tart base and bake! Remove the pan from the heat, stir in the butter and orange zest. Pour the filling into the crust and bake the tart until the curd is firm, with just a slight wobble in the centre, 12 to 15 minutes. Cool completely at room temperature, then refrigerate for at least 2 hours until the filling is completely set.
Decorate! Decorate the tart as you would like. A liberal dusting of powdered icing sugar would be beautiful in its simplicity. Or decorate with seasonal fruit such as red currants, such as I did.