Preheat the oven to 400°F.

Peel and thinly slice 2 large onions.

Heat ⅓ cup olive oil in a large pot over medium. Add the onions and 2 teaspoons salt. Cook, stirring often, until the onions begin to soften about 5-7 minutes.

While the onions cook, slice 1 ½ lbs yukon potatoes crosswise about ⅛” thick.

After the onions have been cooking for 7 minutes, add the potatoes to the pot. Continue to cook, stirring often, until the onions are sweet and soft but not brown and potatoes are just barely turning tender, 7-8 minutes longer. Transfer to a large bowl.

Finely grate the zest of 1 ½ lemons into the bowl. Squeeze in the juice of all 3 lemons. Stir well to combine. Let cool 5 minutes.

Crack 3 eggs into a small bowl, season with 2 more teaspoons salt, and whisk vigorously. Combine eggs with the onion/potato mixture stirring well.

Melt 6 tablespoons of butter. Lightly brush a small baking dish with butter. Lay one piece phyllo on the bottom. Brush lightly with butter. Top with another piece of phyllo. Continue this until there is an 8 layer stack on the bottom.

Pour the potato onion mixture over the phyllo, spreading it out evenly. Continue layering remaining sheets of phyllo.

Brush the final layer in butter and scatter ¼ cup sesame seeds over top. Score the puff pastry in a triangular grid pattern.

Bake for 30 minutes, then tent with foil and continue to cook for 15 minutes until golden and crisp. Move to the bottom of the oven and cook 5 minutes longer.

Let cool at least 20 minutes before serving.