In a food processor, pulse macadamia nuts, brown sugar, and granulated sugar until finely crushed. Add flour and salt and pulse to combine. Add cold butter, one tablespoon at a time, pulsing until the mixture forms a sticky dough.
Press the dough evenly into the bottom of a 9-inch tart pan with a removable bottom or a springform pan. Bake in a preheated oven at 375°F (190°C) for 15-18 minutes, or until lightly golden brown. Remove from the oven and let cool on a wire rack for 10 minutes. Carefully remove the tart from the pan and allow it to cool completely.
Once the crust is completely cool, spread the lemon curd evenly into the tart shell.
For the optional whipped cream topping: In a clean bowl, beat the heavy cream with vanilla sugar (or granulated sugar) on high speed for 2-3 minutes, or until soft peaks form. Spoon or pipe the whipped cream over the lemon curd filling.
Slice and serve immediately. Enjoy!
Notes
This tart is best served chilled. You can make the crust and filling a day in advance.