Mix the flour, salt and yeast in a bowl. Add the butter and milk, knead into a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1 1/2 hrs. until doubled in size.
Halve the dough, shape the two halves into 70 cm long strands that are thinner at the ends. Wrap the strips of bacon around the dough strands. Plait the loaf. Place on a baking tray lined with baking paper, mix the egg yolk and milk. Brush the plaited loaf with half of the mixture, leave to rise for a further 30 mins. Brush the loaf with the remainder of the egg wash before baking.
Approx. 35 mins. in the lower half of an oven preheated to 200°C. Remove from the oven, leave to cool on a cooling rack.