Preheat oven to 160C/325F. Grease two oven trays.
Combine butter, sugar and syrup in a medium saucepan; stir over low heat until sugar dissolves. Cool mixture for 10 minutes. Transfer to a large bowl; in two batches, stir in egg and sifted dry ingredients. Knead dough on a floured surface until dough loses its stickiness. Cover; refrigerate for 30 minutes.
Divide dough into 8 portions. Roll each portion into a 2cm (3/4 inch) thick sausage; cut each sausage into five 6cm (2 1/2-inch) lengths. Place about 3cm (1 1/4 inches) apart on oven trays; round ends with lightly floured fingers, then flatten slightly.
Bake for about 15 minutes; cool on trays.
Meanwhile, make icing. Beat egg white lightly in a small bowl; gradually stir in sifted icing sugar and flour, then enough juice to make the icing spreadable. Place half the mixture in another small bowl; tint with colouring. Keep icings covered with a damp tea towel while in use.
Spread jumbles with pink and white icing; leave to set