Rhubarb & Custard Cookies

1. Preheat the oven to 180°C/350°F.
2. Cream together the butter and sugar in a large bowl until it has a pale colour and light texture.
3. Add the egg and the custard flavouring, then gradually stir in all the dry cookie ingredients until you have a smooth, stiff dough. Wrap the dough in clingfilm and refrigerate for about 15 minutes.
4. Remove from the fridge, divide the dough into 2 pieces and roll each half between two sheets of baking parchment to about the thickness of a £1 coin.
5. Cut out 20 circles and then sprinkle your chosen letter stamps with a little flour and, pressing evenly, stamp your chosen words onto the cirlces. Use the same round cutter to cut out 20 plain cookie circles from the second sheet of dough.
6. Lay the biscuits on baking sheets lined with parchment.
7. Bake for 8-10 minutes until they start to brown at the edges. Remove from the oven, allow to cool a little then place on a cooling rack until cold.
8. Meanwhile, make the buttercream by beating together the butter, icing sugar, milk and rhubarb flavour. Taste and add more rhubarb flavouring if you wish. Stir in a little food colour at a time from the end of a cocktail stick until it reaches your desired shade remember, these food colours are quite strong and it is best to start with a very small amount.
9. Sandwich the biscuits together with a layer of buttercream using plain biscuits as the base and stamped biscuits on top.

Tip: The assembled cookies should stay crisp for up to a week if kept in an airtight container.