In a large bowl, beat together the butter and sugar until well mixed. Add in the egg, egg yolk and vanilla extract and mix again until combined.
Add the flour, cocoa powder, coffee granules, baking soda, cornflour and salt and mix together using a wooden spoon, then prepare 3 large baking trays by lining them with baking parchment or a silicon mat.
Scoop out a heaped tablespoon of the cookie dough, roll into a ball, then squash it flat. Place a Rolo in the middle, then wrap the cookie dough around the Rolo. Roll back into a ball shape and place on the tray. Repeat until all of the mixture is used up (you can put them all on one tray at this point). You should get 20-22 cookies. Place in the refrigerator to chill for at least 2 hours (they can stay in the refrigerator for up to two days like this, but cover them if you’re leaving them in there for more than 2 hours).
When you’re ready to bake the cookies, pre-heat the oven to 170C/325F. Divide the cookie dough balls between the three trays so there’s plenty of space between each one. Place in the oven and cook for 7-8 minutes. Take out of the oven and leave to cool on the baking trays. When cool, drizzle or pipe melted chocolate over the top.
Uncooked cookie dough balls can be frozen on a tray before being placed in a sealed bag in the freezer. Cook from frozen in the same way – just add an extra minute to the cooking time.These cookies should last for 2 days stored at room temperature in a sealed container..Nutritional Information is per cookie.