In a large mixing bowl or the bowl of a stand mixer, stir together the lukewarm water, sugar, yeast, oil and salt.  Let the yeast proof for about 5 minutes until it starts to get foamy.

Add the flour to the yeast mixture and knead with the mixer until smooth.  This could also be done by hand or just using a rubber spatula, but I just thought it was easier to let the dough hook do the work.  

Cover dough tightly with plastic wrap and allow it to rise for 1 hour at room temperature until the dough has doubled in size.  Coat your hand lightly in cooking spray and punch down the dough to remove gas bubbles, then cover again and let the dough rise another 20 minutes.

During the last rise, mix together the filling ingredients in a small bowl.

When the dough is ready, turn it out onto a floured surface and coat your hands with flour (it's a very sticky dough to work with).  Divide into 8 equal-sized pieces and shape into balls.  

Working with one dough ball at a time, flatten it out and mound about a tablespoon of the filling in the center.  Then pinch the edges of the disc together up around the filling, enclosing it completely in the center of the ball of dough as seen in the pictures.  Repeat with the remaining balls of dougha and filling.  You may need to re-flour your hands between dough balls if the dough starts sticking too much.

Heat a large pan over medium heat.  When hot, add a little oil (about 2 tablespoons) to the pan and let that heat up as well.  When the oil is hot, place a dough ball in it, with the sealed area down and cook until lightly golden brown on the bottom (just about 30 seconds), then flip.  Using a large, flat spatula, press down on the hotteok to flatten it into a wide disc and cook until the bottom is golden brown.

Flip the hotteok one last time and reduce the heat to low.  Cover the pan with a lid and cook for another minute or so, just until the bottom is completely golden brown and the filling inside is melted and syrupy.

You can cook more than one hotteok at a time if your pan is large enough.  Just make sure to leave enough space between each dough ball so that it can be pressed flat into a disc.  I can do three at a time in my largest cast-iron pan.

Serve hot!