Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the sugar, brown sugar, and vegetable oil. Mix well.
Add the eggs and vanilla extract to the mixture. Beat until smooth.
In a separate bowl, sift together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the chopped nuts, if using.
Pour the batter into a greased baking dish and spread evenly.
Bake for 30 minutes or until a toothpick inserted into the center comes out clean.
Allow to cool before cutting into squares and serving.