Preheat oven 375º and grease a large baking sheet.
melt butter and add onions and cook until translucent, remove from heat and let cool.
In large bowl, combine potatoes, flour, eggs salt and pepper. Knead until combined well and is smooth.
Divide the mixture into 28 balls, each measuring about 2 inches. Flatten balls slightly and top each with about 2 teaspoons of cooked onions.
Pull enough of the potato dough up over the onion filling to enclose it.
Place the knishes about 1 inch apart on the baking sheet.
Bake 30 to 35 minutes until golden brown.
Serve hot with Dijon mustard, ranch dressing, chili sauce for dipping.