Preheat your oven to 180°C. Line two large baking sheets with baking parchment.
In a mixing bowl, combine the flour and salt. Add the softened butter. Stir in the orange zest and caster sugar.
Add the egg yolks and mix with your hands. Knead for about 3 minutes until you have a soft dough.
Dust your work surface with a little icing sugar. Roll the dough out to a thickness of about 3mm. Use your favorite cookie cutters to cut out shapes. Re-roll the offcuts to make more biscuits until the dough is used up.
Place the shapes on your prepared sheets, leaving about 1cm between them. Bake for 12–15 minutes until they are just golden but not brown.
Let them sit on the tray for a minute, then carefully transfer them to a wire rack to cool completely.
While the biscuits cool, whisk the icing sugar, orange juice, and zest in a small bowl until smooth and glossy. Spread or drizzle the icing over the cooled biscuits and add your sprinkles.