Preheat oven to 180°C / 350°F (160°C fan-forced). Line 2 trays with paper.

Cream butter - Place butter, vanilla and icing sugar in a bowl. Beat for 1 minute until smooth and fluffy (start on low to avoid an icing sugar cloud-storm).

Dry in 3 lots - Stir in cornflour and flour in 3 lots using a rubber spatula. (ie add 1/3 of flour + cornflour, stir in, repeat twice more).

Scoop 1 tablespoon of the mixture onto the trays (cookie scoop handy here), then roll into balls using lightly floured hands (to prevent it from sticking). You should have 24 - 28 balls.

Bake - Press down into 1 cm / 0.4" thickness using a fork. Bake for 15 minutes, switching the trays at the 10 minute mark. Fully cool on trays.

Sandwiching - Pipe frosting onto half the melting moments, then sandwich with remaining cookies.

Set - Refrigerate for 1 hour to set the frosting (else it's so soft, it squirts out!). Then remove from the fridge 30 minutes prior to serving.

Cream butter - Place butter in a bowl and beat with an electric mixer on medium high for 1 minute until smooth and fluffy. Add 1/3 of the icing sugar, then beat in starting on low and increasing to high (to avoid snow-storm!). Repeat another 2 times.

Beat 2 minutes - Add lemon zest and juice. Then beat on high for 2 minutes until fluffy. Transfer to piping bag, snip end off to make a 1cm / 1/2" hole. Use per recipe.

Same method as above for lemon icing.