Zrazi (картофельники)

I grew up eating these, and just discovered my hubby was deprived his entire childhood.  What a shame! I'll have to keep making them to make up for all the lost time.

Filling
1 lb ground beef
1 onion, chopped
1 c chopped portabella mushrooms
salt + pepper
1 tbsp oil

Dough
4 large potatoes
2 tbsp butter
1 egg
salt + pepper
3 tbsp flour

For the final product
1 cup flour
2 tbsp oil, per batch

Make the filling by heating the oil in a pan on medium-high heat. Add in the chopped onions and fry until they turn golden/caramel color.  Add in the mushrooms, and cook while stirring for 3 minutes.  Add in the meat, and fold in, stirring slowly.  Cook until beef is ready, about 5-7 minutes.  Season and set aside to cool.

Boil peeled and cubed potatoes in salted water, until fully softened.  Drain and mash with butter, until smooth.  Sift in the flour and add in the egg. Mix and season with salt and pepper.  Let cool completely.

Spread flour on a working surface.  Drop a heaping spoonful (a wet spoon helps) of the potato mixture and flatten a bit, and flip over.  Flatten into a circle about 1/4 inch in thickness.  Drop 1-2 teaspoonfuls of the filling into the center of the circle.  Carefully pinch the circle together and roll in flour.  Set aside and repeat until all your dough/filling is used.

Fry in batches (with oil), on medium-high heat until a golden crust forms, on each side.