Preheat oven to 350F/180C. Line an 8” pan with parchment paper or you can grease and flour it instead. Keep aside.
In a bowl, sift the flour, salt, and baking powder. Keep aside.
In a different bowl, add the butter, oil, milk, and sugar, beat until smooth in texture. Add the egg and vanilla, beat until combined.
Add the dry ingredients to the wet and mix gently. Pour into the previously prepared pan. Gently place the halved strawberries and the whole blueberries on the batter.
Bake for 10 minutes then reduce heat to 325F/165C and continue baking until golden in color and a skewer inserted in the middle of the cake come out clean.