1. Line a large baking tray with baking parchment.
2. In a large mixing bowl, use an electric hand-held whisk or wooden spoon to cream the butter and sugar together until it is smooth and pale in colour. Stir in the lemon zest and vanilla paste then cut open the tea bags and sprinkle the contents into the mixture as well.
3. Mix in the flour very gently, taking care not to over-work the mixture as this will make the biscuits very chewy. Using your hands, take the dough and knead it gently into a ball with your palms. When it forms a smooth ball, wrap in cling film and chill in the fridge until you are ready to use it.
4. Preheat the oven to 180°C/160°C fan/gas 4. Roll the dough out to a 5mm thickness and use a 5cm round cutter to cut out 30 discs. Arrange on the lined baking tray and bake for 10–15 minutes or until the edges are just starting to turn brown. Allow to cool on the baking tray for a few minutes before transferring to a cooling rack.
5. Make the marshmallows using cool Earl Grey tea as the liquid then use an oiled spatula to spoon it into a large piping bag. Snip the tip off the bag and pipe tall peaks of marshmallow onto the top of each biscuit and leave to set for one hour before the next step.
6. Melt the dark chocolate (you could temper it if you want a more professional finish) in the microwave or in a heatproof bowl over a pan of simmering water. Dip the teacakes in the melted chocolate, marshmallow side down. Sprinkle over the lemon zest and allow the chocolate to set before enjoying. These are perfect served with a cup of tea.