In bowl, combine flour, baking powder, baking soda, and salt. Set it aside. Spray baking pan with oil and lightly dust with flour. Set the pan aside. Preheat the oven to 350°.
In the mixing bowl, combine sugar, vegetable oil, butter, eggs, egg yolks, and ube extract. Beat until all ingredients are well-incorporated.
Add the sour cream. Beat together.
Gradually add the flour mixture into the bowl while beating everything together.
Add in the milk and finish mixing all together.
Transfer the cake batter into the pan. Bake it in the oven for 25-30 minutes. Test the cake with a clean toothpick.
Place in a rack to cool completely.
Beat together the butter, confectionery sugar, salt, and vanilla extract(optional).
Frost the cooled cake.