I have an easy shortbread recipe given to me many years ago when I was a student, by my Scottish landlady, and this would go really well with the caramel. You must use butter for these to get the lovely flavour.
350g plain flour
110g caster sugar
100g dessicated coconut -optional
Preheat oven 180C/gas4
Cream the butter and sugar either by hand or with electric mixer on a low speed till nice and smooth. Sift the flours together and add to the mixture. Work the flours in by hand. Knead the dough till it's smooth then wrap in clingfilm and chill for about 30 mins.
On a lightly floured surface, roll the dough out to about 5mm and cut out rounds with a cutter, the size depending on how big you want your biscuits!
Put the biscuits on baking sheets and bake for 10-12 mins till lightly coloured.
Cool on a wire rack.
When cold, spread one shortbread with some caramel right to the edges and top with another one. Press together very gently, as they break easily.
Hadn't thought about using shortbread to make double biscuits, but will now think of some other filling ideas to try.