1. Prepare the Dough: Combine the flour, sugar, yeast and salt in a large zipper-lock bag. Add the butter, seal and shake to evenly coat the butter. Press the air out of the bag and reseal. Roll over the bag several times with a rolling pin, shaking the bag after each roll, until the butter is pressed into large flakes. Transfer the mixture to a large bowl and stir in the sour cream, orange juice, water and egg yolk until combined.
2. Turn the dough onto a floured surface and knead briefly to form a smooth, cohesive ball. Roll the dough into a 20x12-inch rectangle. Starting at the short end, roll the dough into a tight cylinder. Pat the cylinder flat into a 12x4-inch rectangle and transfer to a parchment paper-lined rimmed baking sheet. Cover with plastic wrap and freeze for 15 minutes.
3. Prepare the Filling: Line a 12-cup muffin tin with liners and grease with non-stick cooking spray. In a medium bowl, stir together the sugars, orange zest, cinnamon and vanilla.
4. Remove the dough from the freezer and place on a lightly floured surface. Roll the dough into a 20x12-inch rectangle and sprinkle evenly with the filling, leaving ½-inch border around the edges. Lightly press the filling into the dough. Starting at the long end, roll the dough into a tight cylinder and pinch lightly to seal the seam. Trim ½-inch of dough from each end and discard. Cut the cylinder into 12 equal pieces and transfer cut-side-up to the prepared muffin tin. Cover loosely with plastic wrap and refrigerate for at least 4 hours or up to 24 hours.
5. Preheat oven to 200 degrees F. Once the oven reaches temperature, turn it off. Remove the muffin tin from the refrigerator and discard the plastic wrap. Place the buns in the turned-off oven until puffed and doubled in size, 20 to 30 minutes.
Remove the buns from the oven and heat the oven to 425 degrees F. Bake for 5 minutes, then reduce the oven temperature to 325 degrees F. Bake until the buns are deep golden brown, 40 to 50 additional minutes. Allow the buns to cool in the muffin tin for 5 minutes, then transfer to a wire rack and remove the liners. The buns are best served warm, but can be stored in an airtight container at room temperature for up to 2 days.
Make Ahead: After placing the buns in the muffin tin, place the tin in the freezer until the buns are firm, about 30 minutes. Transfer the buns (with the liners) to a zipper-lock bag and freeze for up to 1 month. To finish, return the buns to a muffin tin and refrigerate for at least 8 hours or up to 24 hours, then proceed with step #5.