Preheat the oven to 180ºC/160ºC fan-forced. Grease a 30cm x 20cm baking dish and line base and sides with baking paper.
Place carrot, sultanas, pecans and ginger in a large bowl. Whisk oil, eggs, caster and brown sugars in a large jug. Add oil mixture to carrot mixture and stir to combine.
Place flour, spices and tea leaves (discard the bags!) in a medium bowl. Stir to combine. Add dry ingredients to carrot mixture and stir until just combined. Pour batter into prepared dish. Bake for 30 minutes or until a skewer inserted in the centre comes out clean. Stand for 10 minutes before transferring to a wire rack to cool.
Using electric beaters, beat cream cheese, mascarpone, vanilla and half the extra mixed spice in a bowl until smooth and combined. Gradually beat in sifted icing sugar until smooth. Refrigerate until required.
Once cake has completely cooled, spread top with mascarpone frosting and dust with remaining mixed spice. Serve.
Notes
Store cake, covered, in the refrigerator. Best made the day before required.