Place evaporated milk over low heat in a medium size pan until warm.
Beat egg yolks until thick and light lemon color, add sugar gradually. Remove milk from heat and gradually add to yolks while beating.
Return to pan and place over low heat, stirring, until foam in the surface dissapears. Remove from heat before it boils (mixture must not boil). Add butter and mix. Pour in a bowl, cool and transfer to freezer.
Beat heavy cream as for chantilly and fold into cream from freezer. Return to freezer for 8 hours.