Pre-heat your oven to 190°c (170°c for fan-assisted ovens or Gas Mark 5) and grease a couple of baking sheets with a little butter.
In a large bowl, cream the sugar and butter until light and fluffy.
Add the egg and mix until combined. Add the treacle and mix through.
Sift in the flour and add the sultanas. Mix until you have a soft sticky dough.
Take 1-2 tbsp of the dough and roll into a ball, before placing onto your pre-greased baking sheets. Repeat with the rest of the dough, leaving spray between each bun.
Gently flatten each bun a little before baking in your pre-heated oven for 15-20 minutes.
Allow to cool on the baking sheets a little before transferring to a wire rack to cool completely.