If you prefer softer icing whip the butter and icing sugar with a hand held electric whisk, for harder icing add more icing sugar and a few drops of liquid. You can add some lemon juice or vanilla essence to icing if you prefer a less buttery flavour.
Method:
Set oven at 180 degrees (or 150 in a fan forced oven). Grease two baking trays or line with baking paper.
Soften butter (do not melt) I usually microwave it for 15-20 seconds.
Sift dry ingredients and rub in butter, work into a stiff dough.
Roll into balls (approximately 1 teaspoon in each) and place on oven tray. Using a fork, flatten each ball slightly to give the fork indentation. Try and keep all of the biscuits a similar size.
Bake for 8-10 minutes (depending on oven and size of biscuits).
Cool biscuits on cake cooling trays and sandwich together in pairs with butter icing. If I have time or if I am making these for a special occasion I pipe the icing in the middle of the biscuit.
Recipe by Planning With Kids at https://planningwithkids.com/2010/07/05/yo-yo-biscuits-recipe/