Sprinkle the yeast over 1/4 cup of warm water in a small bowl and stir in 1 teaspoon of sugar. The water should be no more than 100 degrees F (40 degrees C).
Let stand for 5 minutes until the yeast softens and begins to form a creamy foam.
Sift together the flour and salt.
Cut in 3/4 cup butter with a knife or pastry blender until the mixture resembles coarse crumbs. Bring the milk to a boil; remove from the heat and stir in 1/2 cup sugar. Cool until the milk is lukewarm, no more than 100 degrees F (40 degrees C).
Pour the milk and yeast mixture into the flour.
Add the eggs and mix well to form a soft, sticky dough.
Turn the dough out onto a well-floured surface and knead until smooth and elastic, about 8 minutes.
Add more flour a tablespoon at a time, if necessary.
Place the dough in a buttered bowl, turning to coat the dough. Cover with a light cloth and let rise in a warm place (80 to 95 degrees F (27 to 35 degrees C)) until doubled in volume, about 1 1/2 hours.
Roll the dough into a square on a floured surface.
Brush the dough with the melted butter and sprinkle with the remaining 1/4 cup sugar and the raisins.
Roll up the dough to form a log, pinching the seam to seal.
Preheat an oven to 375 degrees F (190 degrees C). Grease a 9x13-inch baking pan.
Cut the log into slices about 1 1/2 inches thick.
Place the slices in the prepared pan and let them rise for 30 minutes. Beat the egg yolk with 2 tablespoons of water to form an egg wash.
Brush the buns with egg wash.
Bake in the preheated oven until the buns are golden brown and the centers are set, about 25 minutes.
