1) Combine all of the dough ingredients in a mixing bowl, and mix and knead (by hand, mixer, or bread machine) to make a smooth dough. the dough will seem very dry at first; resist the urge to add more liquid. It'll come together and smooth out as you knead.
2) Place the dough in a lightly greased bowl or other container, cover it, and allow it to rise for 90 minutes. It won't look risen at all. That's OK.
3) Divide the risen dough into two pieces. Working with one piece at a time, flatten/pat/roll it into a 10" x 15" rectangle.
4) Make the filling: Gently beat together the cream cheese, butter, sugar, salt, flavor or extract, and flour till smooth. Add the egg, and again gently beat until only a few small lumps are visible.
5) Spread half the jam/flour (or ClearJel) mixture (about 5 1/2 ounces) in a 2 1/2"-wide swath down the center of the rectangle, lengthwise. Leave 1" of dough bare at each end.
6) Spread half the cream cheese mixture (about 6 1/4 ounces) atop the jam.
7) Fold the end over the filling at each end of the dough.
8) Make cuts from the edge of the dough to within about 1/2" of the filling, every 3/4", all the way down both sides of the dough.
9) Starting at one end, pull the cut strips up and over the filling, alternating sides. Transfer the loaf to a lightly greased or parchment-lined baking sheet.
10) Repeat the process with the remaining piece of dough.
11) Cover the loaves, and let them rise for 90 minutes. Again, it won't appear to rise; that's OK. Towards the end of the rising time, preheat your oven to 350°F.
12) Combine the reserved egg white with 1 tablespoon water, and brush it over the loaves. Sprinkle with the coarse sugar.
13) Bake the coffeecakes for 32 to 36 minutes, until they're golden brown.
14) Remove from the oven, and place on a rack to cool slightly. Serve warm.