Coimbra style sponge cake recipe

Preheat the oven to 150°C. Separate the egg whites from the yolks. Combine the egg yolks with the sugar until the mixture becomes pale. Gradually add the flour. Whip the egg whites with a pinch of salt until stiff peaks form. Gently fold them into the mixture. Grease and flour the pan, then add the mixture. Bake for 55 minutes at 150°C. Note: do not set the oven temperature higher than 150°C. Do not open the oven door while baking.