In a small saucepan heat milk to simmering and remove from heat. Mix in the butter and stir until melted. Let cool until lukewarm.
In a large bowl, mix flour, sugar, yeast and salt. Stir lukewarm milk into flour mixture until a soft dough is formed. Turn dough out onto a lightly floured surface and knead until smooth and elastic, about 5 minutes. Lightly oil a large bowl, place the dough in the bowl and turn to coat with oil. Cover with a damp cloth and let rise in a warm place until doubled in volume, about 1 hour.
Deflate the dough and turn it out onto a lightly floured surface. Knead in raisins and shape into a large round loaf. Place the loaf on a lightly greased baking sheet, cover with a damp cloth and let rise until doubled in volume, about 60 minutes.
Preheat oven to 375 degrees F (190 degrees C). In a small bowl, beat together egg yolk and water.
Brush risen loaf with egg yolk mixture. Bake in preheated oven until loaf is golden and bottom sounds hollow when tapped, about 40 minutes. Transfer to a wire rack to cool.