Mix milk, butter, sugar, and salt and cool to lukewarm. Pour warm water into a warm mixing bowl, sprinkle in yeast, and stir to dissolve. Add cooled mixture, eggs, and 3 cups flour and beat well. Mix in remaining flour and knead lightly on a lightly floured board until elastic. Shape into a ball, turn in a greased bowl to grease all over, cover with cloth, and let rise in a warm, draft free place until doubled in bulk, about 1 hour.Punch down, roll 1/2” thick on a lightly floured board, and cut in rounds with a 3” cutter. Arrange 1 1/2” apart on greased baking sheets, cover, and let rise in a warm, draft free place, until double in bulk, about 1/2 hour.Combine filling ingredients and mix well.With thumb, make a depression in the center of each roll and fill with about 2 teaspoons prune mixture. Let rise 15 minutes.Meanwhile, preheat oven to 400 F. Bake 12 to 15 minutes until golden brown. Transfer to wire racks, brush with melted butter, and dust with sugar.Note:Dainty tea-size kolache can be made by rolling dough into 3/4” balls; let rise as directed, make thumbprints in center, and fill with preserves; bake as directed. Or dough can be rolled into a 12' x 15” rectangle, cut in 3” squares and spread with preserves, leaving 1/4” - 1/2” margin all round; fold corners in toward center until points touch, then pinch to seal. Let rise and bake as directed.