Preheat the oven to 180C / 350F / 160C fan forced. Have a 24 hole non-stick mini muffin tin at the ready (if your tray is not non-stick you’ll need to grease and flour each hole)
In a stand mixer with paddle attachment, beat together the butter and sugar. Add the vanilla and beat well.
Sift together the flour and cornflour then add it to the butter mixture in 3 parts, gently mixing between each until just incorporated.
Use a small cookie scoop to divide the dough among 20 of the muffin tin holes.
Bake for 20-22 minutes until they are just golden around the edges. Leave to cool in the tray before using a knife to very gently pry them out. Make sure they are totally cool before you ice them.
For the Passionfruit Icing
Mix together all ingredients into a smooth icing. Spoon the icing over the cooled cookies, allow them to set for a few minutes and then repeat for a thicker coating.
Notes
I use a standard Australian 20ml tablespoon (= 4 teaspoons worldwide)
For best results you should always weigh ingredients like flour and sugar. Kitchen scales are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).
All ovens vary. Check for doneness 3-4 minutes before the recipe suggests