For the dough: in the bowl of a stand mixer with the whisk attachment, whisk the egg yolks, whole egg, sugar, butter, and buttermilk. Add approximately 2 cups of the flour along with the yeast and salt; whisk until moistened and combined. Remove the whisk attachment and replace with a dough hook. Add all but 3/4 cup of the remaining flour and knead on low speed for 5 minutes. Check the consistency of the dough and add more flour if necessary; the dough should feel soft and moist but not sticky. Knead on low speed 5 minutes more or until the dough clears the sides of the bowl. Turn the dough out onto a lightly floured work surface; knead by hand about 30 seconds. Lightly oil a large bowl. Transfer the dough to the bowl, lightly oil the top of the dough, cover and let double in volume, 2 to 2 1/2 hours.
For the filling, combine the 8 ounces of sugar, lemon zest, fresh ginger, the 2 tablespoons candied ginger and the 5 ounces flour in a medium bowl. Mix until well combined. Set aside until ready to use.
Lightly grease a baking sheet and set aside. Turn the dough out onto a lightly floured surface. Roll into a 12 by 24-inch rectangle. Brush the 1-ounce of melted butter onto the dough and sprinkle the filling over the dough; press the filling lightly so it sticks to the dough. Beginning with the long edge nearest you, roll the dough into a tight cylinder. Brush the beaten egg along the edge for a secure seal. Firmly pinch the seam to seal and roll cylinder seam side down. Brush the 2 ends with a little of the beaten egg and bring together to shape into a ring and firmly press together. Place on the baking sheet, cover with plastic wrap and refrigerate overnight or up to 16 hours.
Remove the ring from the refrigerator, remove the plastic wrap and snip the top with scissors every 2 inches. Place in an oven that is turned off. Fill a shallow pan 2/3 full of boiling water and set on the rack below the ring. Close the oven door and let the dough rise until the ring looks slightly puffy, approximately 30 minutes. Remove the ring and the shallow pan of water from the oven.
Preheat the oven to 350 degrees F.
When the oven is ready, place the ring on the middle rack and bake until golden brown, or until the internal temperature reaches 190 degrees F on an instant-read thermometer, approximately 30 minutes.
While the ring is baking, make the glaze by combining the jam, 1-ounce candied ginger, and the water in a small saucepan over medium heat. Bring to a simmer. Stir and cook until the jam is melted and well mixed with the water, about 3 to 5 minutes. Continue to simmer until reduced and thickened slightly, about 3 to 5 minutes. Brush over the warm ring. Serve immediately.