Make the poppy seed filling: Use a spice grinder or a food processor to pulse the poppy seeds for about 30 seconds. You can do this in batches if needed, but I added them all at once. Add the seeds to a medium bowl, then the boiling water along with the rest of the filling ingredients. Mix well and set aside to cool.
Make the dough: In the bowl of your mixer, add the warm milk, then sprinkle the yeast over the milk. Give it about 5 to 10 minutes for the yeast to bloom, then add the flour, yeast, sugar, salt, milk, oil, and egg to the bowl, and mix for a few minutes to combine the ingredients. Let the hook knead the ingredients, adding a bit of extra flour if the dough it too sticky, until the ball of dough comes clean off the sides of the bowl.
Let the dough rise: Cover the bowl with the dough with plastic wrap and let it rise in a warm environment for 30 minutes to an hour or until doubled in size. Meanwhile, line a baking sheet with parchment paper.
Fill the dough: Roll the dough to a 14"x16" rectangle. Spread the filling, leaving about a ½" border of dough on the edges. Roll the dough starting at the 14" end. Pinch the edges and tuck the ends under the roll to seal the filling inside. Place the roll on the prepared baking sheet and rise for another 30 minutes to 1 hour or until doubled in size.
Bake the roll: Preheat the oven to 350℉. Brush the roll with egg wash and sprinkle turbinado sugar, if preferred, over top. Bake for 35 minutes or until golden brown and cooked through.