1. In a large pan on low flame, cook diced onions with oil salt, pepper, and brown sugar for one and a half to two hours. Drain oil when done and let cool (can also stay in fridge overnight).
2. Preheat the oven to 350 degrees Fahrenheit. Grease a round or oval oven-to-table dish.
3. Flour your surface and roll out the pastry dough.
4. In a bowl, mix egg into the cooled onions and spread down the center of the puff pastry sheet, lengthwise. Carefully roll up the dough.
5. Lay the roll in a spiral shape inside the oven-to-table dish. Place pearl onions in any open spots and cover with any leftover pastry dough.
6. Brush the top of dough with beaten egg yolk and sprinkle with minced onion and sesame seeds.
7. Bake for approximately an hour to an hour and a half or until golden brown.
The easiest way to peal the pearl onion is to cut of the top of the onion, place in boiling water for one minute and cool in ice water or cold water. Use your fingers to pinch the stem end of the onions and the skin will loosen and then slide right off.