In a large bowl, mix the butter, caster sugar, three yolks and vanilla with a wooden spoon until creamy. Stir in the ground rice and flour – you may need to get your hands in at the end to get all of the dry ingredients incorporated. Roughly divide the mixture into 3.
Lay out 3 large sheets of greaseproof paper, and on each one, roll out a third of the dough into a long, thin sausage – about 1in thick. Use the paper to help you to roll it out as smoothly and evenly as possible. Lightly beat the egg white, then brush all over the dough. Scatter over the preserving sugar and roll so the dough is completely coated. Wrap up in the paper and carefully transfer to the fridge to chill for 30-40 mins until firm. At this stage you can freeze for up to 2 months, wrapped well in cling film.
Heat oven to 200C/180C fan/gas 6. Using a sharp knife, slice each roll into roughly 20-30 small biscuits. Arrange over baking parchment-lined baking trays – they will spread a little so leave gaps. Bake for 8-12 mins until pale golden. Cool on the trays until firm. Can also be frozen at this stage for up to a month.
Printing off labels
If you like the labels in the picture, you can print them off here. Simply cut them out and fold each one in half across the dotted line. Staple to the top of a small cellophane bag.
Making your cookies ahead
Make up to 2 months before if freezing, or up to 4 days before if using straight away, and store in an airtight container. You can package up to 4 days ahead if you're using airtight packaging, like bags. If you're worried about guests with allergies, it's a good idea to list all the ingredients on the label.
All the packaging we used to present our favours is easily available on the high street. Head to the haberdashery section at John Lewis for ribbon, string, parcel labels and butterfly clips. Visit Confetti stores, or shop online at confetti.co.uk, for all boxes, bags and lollipop buckets. Our cookies are wrapped in medium cellophane bags (45 x 85 x 220mm), £4.99 for 50.