The Best Soft Chocolate Vanilla Castella Cake (Super Fluffy & Jiggly)

Makes 1 (8-inch cake pan with removable loose base)Ingredients:(A)75g cake flour or 50g plain flour + 25g corn flour sieved60g vegetable oil or mild olive oil for baking (heat to 80C)50g whole or semi skimmed milk5 large egg yolks, cold1 tsp vanilla extracta pinch of sea salt(B)5 large egg whites, cold1/2 tsp white vinegar / lemon juice70g golden granulated sugar, optional (add sugar a little at