In the bowl of a stand mixer fitted with a paddle attachment, combine flour, sugar, salt, sour cream, butter, egg yolk, vanilla extract, water and yeast. With mixer on medium speed, knead ingredients together until dough is well combined and smooth.

Place dough in a lightly oiled bowl. Cover with plastic wrap and let dough stand at warm room temperature for 90 minutes. The dough will not appear to have risen.

Remove dough from bowl and divide into two pieces. On a piece of parchment paper, roll one piece of dough into a 10x15-inch rectangle. Spread half the chocolate spread down the center of the rolled dough. Top with half the cherry preserves. Fold both ends of the dough over the end of the filling.

Make cuts from the edge of the dough to within 1/2-inch of the filling, every 3/4-inch, down both sides of the dough. Starting at one end, pull a cut strip up and over the filling, repeat, alternating sides until you reach the bottom of the loaf. Repeat all steps with second ball of dough.

Transfer dough on parchment paper to baking sheet. Cover loaves and let them rest for 90 minutes.

Preheat oven to 350°F. Whisk together egg white with a tablespoon of water. Brush each loaf with egg wash and sprinkle with coarse sugar. Bake in preheated oven 32-36 minutes until golden brown. Remove from oven to a wire cooling rack. Serve warm.