Mix flour, salt, and sugar in a bowl and rub in the softened butter and yeast with your fingertips.
Make a well, pour in milk and one egg, then bring the mixture together into a soft dough.
Knead the dough on a clean surface for 10 minutes until smooth and elastic.
Place dough in an oiled bowl, cover with a damp towel, and prove for 80 to 90 minutes.
Combine chopped prunes with orange zest and juice and soak for at least 30 minutes.
Beat sugar and cinnamon into softened butter until well combined.
Grease and line a 34x24cm roasting tin with butter and baking parchment.
Knock the air out of the dough and roll it into a 30cm long rectangle.
Spread cinnamon paste over the dough and sprinkle with drained prunes, reserving the juice.
Roll the dough into a sausage shape and cut into 12 equal slices.
Place slices in the tin, cover, and prove for 45 minutes.
Preheat the oven to 200°C.
Brush the tops of the buns with a glaze made from the remaining egg and egg yolk.
Bake at 200°C for 10 minutes, then reduce to 180°C and bake for 20 more minutes.
Boil reserved orange juice and caster sugar for five minutes to create a syrup.
Brush hot buns with syrup and move to a wire rack to cool.