Preheat oven to 325°F. Do not grease your pan.
Beat egg yolks with sugar until thick and pale.
Add oil, lemon zest, vanilla, and salt. Mix gently.
Sift in matzo meal and potato starch. Fold to combine.
Whip egg whites in a clean bowl until stiff peaks form.
Fold whites into yolk mixture in three parts, gently.
Pour into pan, smooth the top, and bake 50–60 mins.
Cool upside down before releasing from the pan.
