Preheat oven to Fahrenheit 350°
Grease and line two 9” cake pans
Cream butter, oil and sugar until soft and creamy
Add 2 egg whites and vanilla and beat mixture until it has increased in volume
Slowly mix in flour, alternately with yogurt, just until mixed in
Finish with milk and vinegar, again stirring just to combine
In a clean separate bowl, beat remaining two egg whites until stiff peaks
Gently fold into batter
Pour batter into two prepared pans, dividing the batter evenly
Bake for 25 minutes, until cake is golden brown and springs back to the touch
Remove from oven and invert on wire racks to cool completely