For the biscuits: In a large bowl, combine the peanut butter, honey, butter and sugar until fully incorporated. Then mix in the egg. (The mixture will look like thick cake batter at this point.) Add half the flour and mix to combine, then add the final half and salt and mix again. Place clingfilm onto the dough, and put into the fridge for 30 minutes to chill.
Liberally flour your worksurface and roll out the chilled dough. Using a 2 1/2inch circle cutter, cut out rounds. Then using a 1 1/2 piping tip cut out circles in the middle of your biscuits, to create rings. Then place them onto a baking tray lined with baking paper. Continue this process until all your dough is used – only re-roll the dough 2-3 times, after that your biscuits may be tough.
Chill the rings on their baking trays in the fridge for 20 minutes until they’re firm to the touch. Meanwhile, preheat the oven to 175C/155C Fan.
Bake the biscuits for 10-12 minutes, until golden brown. Leave the biscuits to cool on the tray for a few minutes, before placing them on a cooling rack.
For the icing: Place the royal icing sugar in a large bowl and add the water in a tablespoon at a time until you reach a thick consistency. (You can use an over-baked/misshapen biscuit to test your icing is the correct consistency – it should stick to the biscuit well but spread evenly when turned.) Then place 1/4 in a small bowl and add your chosen food colouring, repeat this with two other bowls, leaving one bowl (and the final 1/4 icing) for your white icing. Place the white icing in a piping bag and snip off the end to create a small hole.
Hold your biscuits face down into the coloured icing for a few seconds, then place face up on a cooling rack for the icing to set. After a few minutes, pipe the white icing in parallel lines across the biscuit, then using a cocktail stick drag through the icing in alternating directions to create a feathered effect. Leave the biscuits to set on the cooling rack.
Best eaten in the first few days. Biscuits can be kept in an air-tight container for 1 week, but will soften slightly.