Warm the sugar, butter, and milk in a small saucepan until just warm.
Pour into a bowl, stir in yeast, and leave for 10 minutes until foamy.
Mix flour, salt, cinnamon, and lemon zest in a large bowl and make a well.
Whisk egg into the milk mixture and pour into the flour well.
Knead the mixture on a lightly floured surface for 5 minutes until smooth.
Knead the raisins and currants into the dough for 2 minutes.
Place dough in an oiled bowl, cover, and let rise for 1.5 hours.
Knock back the dough and divide into 8 portions shaped into balls.
Place buns on a tray lined with parchment and flatten slightly.
Cover and leave to prove for a further 45 minutes.
Bake in the center of the oven at 190°C for 20 minutes.
Serve warm with butter and syrup or honey.