Preheat oven to 170 ° Celsius. Grease the bottom and sides of 3 , 6 -inch round cake tins and line the bottom with parchment paper.
Sift together flour, salt and baking powder, set aside.
In the bowl of stand mixer beat butter, oil, sugar and vanilla bean paste until light and fluffy, for about 5-7 minutes.
Add eggs one after the other beating well after each addition.
Beat in the yoghurt. Scrape down the sides and the bottom of the bowl as needed.
With mixer on low, alternately add the flour mixture and milk, beginning and ending with flour mixture.
Divide batter evenly between cake tins. (To ensure each tin had the same amount of batter I used a measuring cup and a scale).
Bake for 30 minutes or until tooth pick inserted in centre comes out clean. Leave to cool on a wire rack for 20 minutes, then invert onto a wire rack gently, discard parchment paper and cool completely before assembling.