1. Heat olive oil in a large skillet over medium heat. Add diced onions and sauté until translucent. Lower heat and sauté gently until golden brown, about 20 minutes. Set aside.
2. Line a sheet pan with parchment paper. Preheat the oven to 400 degrees Fahrenheit.
3. Using a fine grater or kugel blade in the food processor, shred the potatoes. In a large bowl, whisk the eggs and salt to combine. Add shredded potatoes and hot oil. Mix well and pour batter into prepared sheet pan.
4. Bake for 45 to 60 minutes or until golden. Remove from oven and let cool 10 minutes. Using the parchment paper to help you roll up jellyroll style and let cool.
5. Gently unroll the kugel and cut in half crosswise. Trim off any crispy edges. You will have two rectangles measuring about six by 18 inches. Cut diagonally to form triangular wedges. Spread sautéed onions on each triangle. Roll up like a rugelach, starting from the small point. Secure with a toothpick.
6. Brush with egg wash and bake until crispy. Remove toothpicks and serve with your favorite dipping sauce.