Heat oil in medium pan over medium-high heat; season brisket with salt & pepper and cook, turning as needed, until browned, 8-10 minutes. Reduce heat to medium and add half the onion; cook until onion is soft and caramelized, 6-8 minutes. Add tomato paste, brown sugar, and garlic; cook 3 minutes more. Add stock and chile flakes and bring to a simmer; reduce heat to low, cover, and cook until meat is falling apart, about 2 hours. Set aside. Heat oven to 375. Place canola oil in a baking pan and put in oven. Bring a large pot of salted water to a boil; cook potatoes 3-5 minutes. Drain and rinse potatoes under cold water; pulse in a food processor until chunky. Transfer potatoes to a bowl with remaining onion, eggs, salt, and pepper. Remove pan from oven and place half of the potato mixture in the bottom, then the brisket, then top with remaining potatoes. Bake until golden and bubbling, about 1 hour 15 minutes.