Preheat oven 170°C.Boiled milk at medium heat. Lower heat add in cheese and butter stir till melted. Leave milk mixture to cool.Add egg yolks into cooled down cheese mixture and mix until well combined. Sift in flour and mix until smooth.Beat egg whites and cream of tartar until frothy. Add sugar in batches and beat till stiff peaks.Fold â…“ of the egg whites into cheese mixture, gently fold well with rubber spatula.Pour cheese mixture into the remaining egg whites, fold it gently with rubber spatula until blended.Pour batter into a 8-inch chiffon cake pan, bang the pan on a hard surface to release air bubbles and bake for 35 - 40 minutes.Invert cake immediately after bake, cool completely on rack before consuming.