Place the butter and flour in a food processor and pulse until you have a sandy mixture.
Transfer to a large bowl, add the icing sugar, egg, vanilla extract and salt.
Mix the ingredients with your hands then turn the mixture onto a work surface and knead until you have a smooth dough.
Wrap the dough with cling film and let it rest in the fridge for 30 minutes.
Place the chilled dough on parchment paper, lightly dust it with flour and roll it out with a rolling pin until is ¼ inch (5 mm) thick.
Lay a tea bag down onto the dough for measurement and cut out rectangles using a knife.
Using again the tea bag for measurement, cut the top corners to give your rectangles a tea bag shape.
Use a decorating tip or a straw to poke a hole at the top.
Put the cookies in the fridge for 30 minutes and preheat the oven to 347°F (175°C).
Bake for 11/12 minutes or until slightly golden then allow to cool at room temperature.
Put the dark chocolate in a narrow container and microwave it in 30 second intervals, stirring frequently, until the chocolate is completely melted.
Dip the tea bag cookies halfway in the melted chocolate and put them on a baking tray lined with parchment paper or on a cooling rack. Place the cookie in the fridge for 10/15 minutes, until the chocolate hardens.
Cut a piece of string (about 9 inches-20 cm long). Thread the string through the hole.
Use a glue stick to cover the blank side of your tag. Place the two loose ends of the thread onto the sticky paper and fold it in half securing the two thread ends inside.