1. Place the flour, oatmeal, salt and bicarb into a large mixing bowl, stir and rub in the butter until it looks a bit like bread crumbs.
2. Stir in the sugar then add the milk and bring the mixture together, squeezing and kneading in the bowl to form a dough.
3. Flatten into a disc, wrap in cling film and place in the fridge for 30 minutes.
4. Line two baking trays with baking parchment. Place the dough between 2 sheets of parchment paper and roll the dough to 3mm thick.
5. Using a 6.5cm straight sided cutter stamp out circles. Place on the prepared trays leaving spaces between. Prick the surface of the biscuits with a skewer or fork and place in the fridge for 20 minutes.
6. Preheat your oven to 190°C/170°C fan/Gas Mark 5. Take the chilled biscuits from the fridge and bake in the oven for 15-20 minutes until golden and crisp. Leave to cool on the tray for 5 minutes before transferring to a wire rack to cool completely.
7. Break the chocolate into small chunks and place in a heatproof bowl set over a pan of simmering water. Once the chocolate has melted remove from the heat. Dip a teaspoon in the melted chocolate and place it on top of one biscuit.
8. Working from the middle to the edge spread the chocolate so the surface is thinly coated. Using a skewer, draw lines across the chocolate horizontally and then vertically to create a pattern on the surface of the chocolate.
9. Repeat on the other biscuits until the melted chocolate is used up. Leave the biscuits until the chocolate has set.