Grease an 8 1/2-inch by 4 1/2-inch nonstick loaf pan with butter.

Dust the surface of the prepared Gluten-Free Brioche Dough with rice flour and pull off a 1-pound (grapefruit-size) piece. Dust the dough with more rice flour and quickly shape it into a ball.

On a flat floured surface, roll out the ball to a 1/4-inch thick rectangle. As you roll out the dough, add rice flour as needed to prevent sticking.

Spread the Nutella evenly over the rectangle, leaving a 1-inch border all around.  Starting with the long side of the dough, gently roll it up into a log. (If it is sticking, gently nudge it along with the aid of a pastry scraper and additional rice flour.) Pinch the seam closed.

With the seam facing upward, bring the ends in toward the center.  Flip over and gently place the prepared loaf into the buttered pan with seam sides down.  Allow it to rest for 60 minutes at room temperature, loosely covered with plastic wrap.

Fifteen minutes before baking, preheat the oven to 350°F.

Brush the top of the loaf with the egg wash.  Sprinkle lightly with the coarse sugar.  (Granulated sugar can also be used.)

Bake for 45 minutes or until the loaf is well set and the top is golden brown.  The bread may break open and reveal the Nutella within.

Remove from the pan and cool completely on a wire rack.