Preheat the oven to 180 C / 356 F.
Prepare sheet pan dish ( 12 x 16 inches ) and cover it with baking paper.
Spray baking paper with vegetable oil and leave the pan aside.
In medium sized bowl, whip egg whites and pinch of salt until firm.
Slowly add sugar, egg yolks, vanilla extract, lemon zest and ground pepitas and combine gently, using spatula.
Pour batter into prepared pan, even it and bake for nine minutes.
Take the pan out from the oven and immediately form a roll cake.
Let it cool completely.
Unroll cold sponge carefully and fill with sour cream.
Roll up again and leave in the fridge for few hours before serving. Overnight is the best.