Preheat oven to 170 ° C. Grease bottom and sides of 3, 6 -inch round cake tins and line bottom with parchment paper.
Sift together flour, salt, baking powder and soda. Set aside.
In the bowl of stand mixer beat butter, oil and sugar until light and fluffy about 7 minutes. Scrape down the sides of the bowl.
Add egg whites, then vanilla extract and beat until combined.
Mix together strawberry reduction and buttermilk.
With mixer on low, alternately add the flour mixture and buttermilk mixture, beginning and ending with flour mixture.
Divide batter evenly between cake pans. ( I used a measuring scale to ensure each cake pan contained the same amount of batter ).
Bake for 25 minutes or until a tooth pick inserted in centre comes out clean. Leave to cakes to cool on wire racks for 10 minutes, then invert onto rack gently, discard parchment paper and cool completely.
Wrap cakes in cling film and chill in the fridge for 1- 3 hours before frosting.