Make the filling as the crust bakes.
Add the egg yolks and the sugar to a medium saucepan – do not turn on the heat just yet.
Stir as you add the pummelo juice and butter.
Now, turn to a medium setting, and cook the mixture as you stir it constantly for about 8 minutes. The curd should thicken enough to coat the back of a spoon as you draw it out – don’t allow it to come to a full boil.
Remove from the heat, and stir in the pummelo zest quickly.
Pour the pummelo curd over the baked crust, using a spatula to spread it evenly.
Return the pan to the oven, and bake for another 16 to 18 minutes. The curd filling should still be a little wiggly.
Remove from the oven, and allow the bars to cool in the pan for about one hour.
Dust with the powdered sugar, and cut into bars.
You can store them up to 3 days in an airtight container at room temperature.