How to Make It
Bring milk to a simmer in a small pot over medium. Remove from heat and add cubed butter, stirring to melt. Let cool until warm to the touch, 5 to 8 minutes. Whisk in eggs.
Whisk flour, yeast, ¼ cup sugar, and ½ teaspoon each cinnamon and salt in a large bowl. Gradually add warm milk mixture, stirring until just combined and no dry spots remain. Transfer to a lightly floured surface; knead dough, flouring surface as needed, until smooth and elastic, about 8 minutes. Transfer to a buttered bowl; cover with plastic wrap. Place in a warm, draft-free spot until doubled in size, about 1½ hours. (At this point, dough may be wrapped and refrigerated for up to 3 days.)
Meanwhile, mix raisins, dates, and bourbon in a bowl, pushing down fruit to submerge. Let stand for 30 minutes. Drain, reserving 1 tablespoon bourbon; transfer to a food processor (discard remaining bourbon). Add orange zest, 2 tablespoons melted butter, and remaining ½ teaspoon cinnamon and ¼ teaspoon salt; pulse until a thick but spreadable paste forms, about 15 times.
Grease a 9-by-5-inch loaf pan with butter. Transfer dough to a lightly floured surface; roll out to a 15-inch square. Spread fruit paste evenly over dough to edges. Roll into a log; cut in half lengthwise to make 2 long pieces. With cut sides facing up, twist dough pieces together to form a long spiral; tuck ends underneath. Transfer to prepared loaf pan. Cover; let rise at room temperature until puffy, 1 to 1½ hours.
Preheat oven to 350°F. Brush top of loaf with remaining 1 tablespoon melted butter; sprinkle with remaining 1 tablespoon sugar. Bake until golden brown, 45 to 50 minutes (tent with foil after 35 minutes, if needed, to prevent loaf from overbrowning). Let cool in pan, about 10 minutes. Remove loaf from pan and transfer to a wire rack. Serve warm or at room temperature. To store, wrap tightly in plastic wrap; keep at room temperature for up to 3 days or freeze for up to 1 month. To reheat, warm slices in the toaster.