Mix together the flour, salt and sugar in a bowl. Crumble in the fresh yeast (or stir in the dried yeast). Rub the softened butter into the flour mixture with your fingertips until there are no large lumps of butter. (It does not have to be as fine as breadcrumbs, as you would do with a crumble.)
Make a well in the flour mixture. Pour the milk into the well and crack in one egg. Bring the dough together with your hands or with a spatula. This is quite a soft, supple dough - if it feels a little wet and sticky, don't panic. Keep mixing and the flour will absorb the liquid.
Turn the dough out onto a clean surface and knead for 10 minutes or until the dough is smooth and elastic. Cut a small piece off and stretch the dough as thin as you can – if you can see light shining through the dough and you can see the shadow of your fingers held behind the thinnest part, it is ready.
Put the dough in an oiled bowl, cover with a damp tea towel and leave to prove for about 80-90 minutes.
Meanwhile for the filling, combine the chopped prunes with the orange zest and juice and set aside. The fruit should be soaked for a minimum of half an hour, but it can be made as much as a day in advance.
In a small mixing bowl, beat the sugar and cinnamon into the softened butter with a fork until well combined. Set aside.
Lightly grease the base and sides of a deep roasting tin roughly 34x24cm/13x9in with butter and line with baking parchment.
When the dough has nearly doubled in size, tip it out of the bowl and knock the air out. Roll the dough into a rectangle, the thickness of a pound coin. The long side of the rectangle should be about 30cm/12in long.
Spread the cinnamon paste over the surface of the dough, ensuring the paste reaches all the edges. Drain the soaked prunes, reserving the juice, then sprinkle the prunes evenly over the dough.
Starting with a long side of the rectangle, roll the dough up into a sausage shape. Flour the work surface and lay the rolled dough on top of the flour before cutting into rolls into 12 equal slices.
Place the slices side by side, with the spiral facing up, into the lined roasting tin. Cover with a damp tea towel and leave to prove again for about 45 minutes.
Preheat the oven to 200C/400F/Gas 6.
When the buns have risen and feel springy to the touch, they are ready to bake. Beat the remaining egg and egg yolk together in a small bowl, and brush the tops of the buns with egg glaze. This will give the buns a shine and lovely colour.
Bake the buns at 200C/400F/Gas 6 for 10 minutes and then lower the oven temperature to 180C/350F/Gas 4. Cook for a further 20 minutes.
While the buns are baking, make the syrup. Pour the reserved orange juice from soaking the prunes into a small saucepan with the sugar. Gently heat the mixture, stirring until the sugar dissolves. Bring the syrup to the boil and cook for five minutes. Set aside.
When the buns have finished baking, remove them from the oven and brush with the syrup so that the orangey flavour soaks right into the buns. Transfer the buns on the paper to a wire rack to cool.