Changes that I made: left out the cheese and rosemary; used regular sesame seeds, baked in a 9″ round silicone pan (lined both bottom AND sides with parchment); baked it a bit longer than the recipe said; and used 3 extra large plus 4 large eggs instead of 10 medium eggs or 8 large eggs. Oh, I forget to measure the amount of oil before adding it to the onion to saute them. I think I added maybe a couple of Tablespoons of oil to the onions and then I added another 4 Tablespoons of oil to the batter.
Changes I would make next time: the red onion is very pretty, but it turn blue-ish green-ish the next day (it is the anthocyanins in red onions, which are red in an acidic environment and green in an alkanine environment, according to Robert Wolke). Regular onions would not have this problem and I would stick to using regular onions if making this ahead.
Overall thoughts: delicious, somewhere between a quiche and a kugel. The cheese would make this even more savory and yummy, but kept dairy-free it makes a nice Shabbos side dish (especially when there are vegetarian guests). Very pretty presentation. Also would make a nice vegetarian main dish with a salad.