Complex sentence: November 1909 saw the stormy premiere of the complex orchestral interlude (entitled "Nachtstück") from "Der ferne Klang", the opera he had been working on since 1903 and in 1912, the first performance of the complete opera in Frankfurt consolidated his fame.
Split into simpler sentences: November 1909 saw the stormy premiere of the complex orchestral interlude (entitled "Nachtstück") from "Der ferne Klang", the opera he had been working on since 1903. In 1912, the first performance of the complete opera in Frankfurt consolidated his fame.