A method and apparatus is disclosed for casting a composite ingot made of metals that are susceptible to surface oxide formation when molten. The method involves co-casting at least two metal layers from at least two molten metal pools formed within a direct chill casting apparatus. During the casting operation, movement of metal oxide formed on the upper surface of at least one of the pools towards an edge of the pool is restrained by an oxide skimmer positioned close to an edge of the pool above an external surface or metal-metal interface of the ingot. The apparatus provides a DC caster with at least one oxide skimmer that operates in this manner.