your choice of coloured sprinkles (we used hundreds and thousands, pink and yellow sugar and some white chocolate stars)
Rub the flour and butter together with your fingertips until it looks and feels like fresh breadcrumbs then add a pinch of salt. In another bowl, mix together the sugar, egg and vanilla extract then pour it over the butter and flour mixture. Gently knead it together then separate the dough into 2 equal blocks. Knead some pink food colouring into one of them and keep the other plain. Wrap both types of dough in sheets of cling film and chill in the fridge for 20-30 mins.
Heat oven to 180C/160C fan/gas 4 and line 2 trays with baking parchment. Roll the plain dough out onto a lightly floured surface until it’s about 25cm long and 20cm wide. Do the same with the pink dough and lay one on top of the other. Lightly roll over the surface once or twice with your rolling pin just to press them together. Trim off all the edges so they're straight then carefully roll them up from one of the short edges to make a tight spiral. Wrap tightly in cling film and chill for 1hr or overnight.
Unwrap the dough, trim the end and cut the rest into 20 slices and lay them cut side down on your prepared baking tray. Bake for 15-17 mins or until ever so slightly golden at the very edges. Allow them to cool on the tray before transferring them to a wire rack to cool completely.
Mix the icing sugar with enough lemon juice to make it the consistency of smooth peanut butter and pour the sprinkles into a shallow bowl or plate. Dip the outside edges of the biscuits into the icing (or spread it onto the edges using the back of a teaspoon) and then into the sprinkles, turning to coat. Leave to set before serving.