To make the potato mixture you first have to fry the onion in the oil in a frying pan. Make sure you fry the onion at low heat and wait until it turns a little brown.
Then in a bowl containing the potatoes add these cooked onions. As your potatoes are already mashed mix them with the onion and sprinkle salt and pepper to season the mixture.
Also, add the dry onion mix to complete the flavoring of the mixture.
The next step is to make Knishes. Take one sheet of dough by flouring a clean surface and then spread the potato mixture on one side as the dough is rolled.
Fold the dough covering the potato mixture and make the shape of a roll.
Cut the remaining end and stick the ends so that the material will not spread out. Repeat the process with the remaining sheet of the dough.
Then to bake the rolls grease the baking pan as your oven is already preheated at 375 degrees.
Before baking brush the blended egg mixture on the rolls to make a good coat over the rolls. Bake for half an hour and your potato knishes will be ready after that half hour.
Before serving, cut each roll into pieces and serve with sides.