First of all, beat the butter in a bowl with a wooden spoon to soften it.
Beat in the sugar, followed by the sifted flour and semolina.
Work the ingredients together with the spoon, pressing them to the side of the bowl, then finish off with your hands until you have a smooth mixture that doesn't leave any bits in the bowl.
Divide the mixture into 9, and shape each portion into a ball (dust the work surface with flour if you find the mixture too sticky to work with).
Flatten each one slightly and prick the centre with a fork (but not all the way through).
To make it look pretty, make a 1 cm crinkly border on the top by lightly pressing a fork making a slight indent working all the way around (working for the edge towards the centre).
Make sure that the biscuits are at least 1/2 inch in thickness (with the indentations at the edges).
Place onto the prepared baking sheet, very well spaced out as they will spread out quite a bit during baking.
Bake them for 50-60 minutes on the centre shelf of the oven (keep an eye on it after 45 mins - the edges seem to colour more easily than the top) – it should have turned pale gold and feel firm in the centre.
Remove from the oven and dust the top with caster sugar.
Leave it to cool for 5 minutes on the baking tray before transferring them onto a wire rack to cool completely.