Pre-heat oven to 200c /180c fan/Gas Mark 6. Cream together the butter and 200g of sugar until pale and fluffy, about 5 minutes.
Add the egg, vanilla, and finely grated easy peeler zest, then mix again to combine. If using a stand mixer, make sure to scrape the bowl down as you combine the ingredients.
Sift together the flour, ground cinnamon, ground nutmeg, baking powder, and salt. Sprinkle the dry ingredients into the mixing bowl, then slowly stir the mixture to combine. Do not mix the dough any more than is necessary, or the biscuits will become tough
Dust the work surface with plain flour. Roll out the dough to about 3mm thick. Cut our 48 large stars. Use a smaller star cutter to make windows in half of the biscuits.
Transfer to a lined baking sheet with a palette knife or hamburger turner. You will need 4 baking sheets for all the biscuits - make the biscuits in smaller batches if necessary.
Move the baking sheets to the fridge for 20 minutes, or to the freezer for 5 minutes. This will harden the butter, and stop the biscuits from spreading too much in the oven.
Bake the biscuits for 7-8 minutes until the edges are starting to brown, then leave to cool on the baking tray for 5 minutes. Transfer to a wire rack and leave to cool completely
Place the easy peeler juice, sugar and lemon juice into a medium saucepan. Bring to a rolling boil, then add the liquid pectin. Maintain the rolling boil for 1 minute, then turn off the heat. Transfer the jelly into a shallow heatproof dish to cool quickly.
Use a whisk to break up the set of the jelly slightly. Place half a heaped teaspoon of the cooled jelly onto one of the base biscuits. Gently press a windowed biscuit on top, and tilt the biscuit to fill the window evenly. Dust the biscuits with icing sugar while the jelly is still wet.
Store in an air tight container - and enjoy!