Preheat fan-forced oven to 160°C (320°F). Grease and line two 8-inch cake tins.
Sift together flour, cornstarch, baking powder, and salt. Whisk to combine.
Mix strawberry reduction, milk, and food colouring in a small bowl; set aside.
In a separate bowl, cream butter, oil, and sugar with a mixer for 3 minutes until fluffy.
Add egg whites in three additions, mixing well between each.
Incorporate half the strawberry-milk mixture, along with extracts and vinegar; mix until uniform.
Fold in half of the dry ingredients using a spatula until just combined.
Add the remaining strawberry-milk blend, fold gently, then add the rest of the dry mixture. Avoid overmixing.
Divide batter evenly between tins and bake for 35 minutes or until a skewer comes out clean.
Cool in tins for 15-20 minutes, then transfer to a wire rack to cool fully.