Serbian Christmas Bread (Sweet Cesnica)

Ingredients (10)

• 2 cups milk (lukewarm, warmed to 105 degrees)
• 4 teaspoons active dry yeast
• 4 tablespoons sugar
• 4 large egg yolks (at room temperature; reserve the whites)
• 4 ounces/1 stick butter (softened)
• 1/2 teaspoon salt
• 5 1/2 to 6 cups all-purpose flour
• 1 cup all-purpose flour
• 1 large egg yolk (room-temperature; reserve the white)
• 1 tablespoon milk (or ​as needed)