Get ready with all the measured ingredients at room temperature.
Sift All purpose flour and salt together for two to three times and keep aside.
In a gas top or microwave melt butter with oil on a low heat.
Add melted butter oil mixture to the sifted All purpose flour and whisk well with a whisk until it forms a smooth flour paste (aka roux).
In a wide dry bowl add egg yolks, milk and vanilla extract and beat well until it is well combined.
In another wide bowl add egg whites and whisk (I used electric hand mixer) until frothy. Now add cream of tarter and continue beating until fine foams form for 2 minutes.
Gradually add caster sugar little by little ( mix 3 portions )until it forms stiff peaks (French meringue) consistency. Keep it aside.
Add egg yolk mixture to the flour butter oil paste( aka roux) and mix well until it forms a smooth paste without any lumps.
Mix ⅓ of the meringue to the yolk batter and mix gently with a spatula. Add meringue little at a time( 3 parts) and gently swirl until no egg yolk streak remain or seen.
Grease only the bottom of the Tube pan and dust well with all purpose flour. Do not grease the sides or the tube of the pan as the cake batter will not be able to cling to rise and fall flat. Preheat oven to 160 °C .
Pour the cake batter in the pan and gently tap the pan side to side to release air bubbles and get even top .
Wrap the base of the tube pan with aluminium foil (purely optional) .Place the tube pan into a cookie tray holding a shallow water bath and reduce the temperature to 150 °C and bake for 50 minutes or until skewer inserted comes out clean.
When the cake is done remove from oven and immediately invert to cool completely before unmoulding. I prefer to sprinkle some icing sugar and garnish it with whole strawberries.
Slice a piece or two and serve with a cup of coffee or milk . Serve with a cup of milk during breakfast or as a dessert with a scoop of ice cream.