Oat and chocolate biscuits

Mix together all the dry ingredients in a bowl, then rub the cold butter into them. Once the melted butter has cooled down, mix in the malt vinegar. Pour the butter/vinegar mixture into the dry ingredients and mix together to form a dough. Squash the biscuit dough between two sheets of baking paper and roll it to about 2mm thick. You want it to be quite thin because you will be sandwiching the biscuits together later so two biscuits =one biscuit in this case. Let the biscuit dough chill for about 20 minutes in the fridge. You want it to be pliable but chilled. Line a large ,flat baking tray with baking paper. Cut out the biscuits and place them on the tray using a 6cm fluted cutter. You can squash all the offcuts together ad infinitum. Bake at 195c/175c fan for around 10 minutes. If they are nit golden by then leave them in for one minute longer at a time. Allow to cool completely on a rack before sandwiching with chocolate. As they are cooling down melt your chocolate over a bain-marie until it is liquid.. Spread about a teaspoonful on to a biscuit and squish another on top. You want to encourage the chocolate to squish out of the edges a little, so add a litle more if you need to. Now leave to set and chill. They will keep in an airtight container for up to 5 days but honestly they will be eaten well before then.