Preheat oven to 180C/160C fan-forced. Grease and flour two 6 x 1 cup capacity muffin pans.

Using an electric mixer, beat egg yolks and lemon curd together in a large bowl for 3 to 4 minutes or until very pale and thick. Add the lemon rind and flour, beating until combined. Add the butter, beating until well combined. With the beaters on low speed, gradually add the sweetened condensed milk and milk. Beat until well combined.

Using an electric mixer and clean beaters, whisk egg whites in a bowl until soft peaks form. Fold a ⅓ of the egg whites into flour mixture. Fold in remaining egg white, in two batches, or until just combined (you may have a few lumps). Pour into prepared pan.

Bake for 20 to 22 minutes or until the pies are firm but mixture is slightly wobbly. Set aside in the pan to cool completely. Serve, dusted with icing sugar.