When Fabian Müller made his Pierre Boulez Saal debut in January 2022, his memorable performance of Beethoven’s monumental “Hammerklavier” Sonata confirmed his reputation as one of the outstanding pianists of his generation. Now the ARD Competition winner, who was born in 1990 in Beethoven’s hometown of Bonn, takes on the challenge of presenting all the composer’s sonatas as a complete cycle. Dubbed the “New Testament” of piano music by Hans von Bülow— Bach’s Well-tempered Clavier was known as the “Old Testament”—the 32 works will be heard over the course of eight Sunday-afternoon concerts.