First time making these, so I made a small trial batch.
1oz icing sugar
1 tsp vanilla essence
Cream margarine, essence and sugar together. Add flour and beat until a stiff dough forms. Pipe in swirls onto lightly greased baking sheet and bake for 18 mins or so at Gas 4/350F/180C
I made half the mix chocolate though so added probably 1 dsp cocoa and an extra tsp water to make up for the extra dry ingredient (cocoa).
When cool sandwich together with jam (I used Strawberry) and vanilla frosting. In the case of the chocolate ones I used a dairy free chocolate spread and vanilla frosting.