The thing is, that these four letters B-A-C-H (in German B means Bb and H - the note B) could serve very well as a subject for a fugue. They form chromatic ascending sequence, they can be inverted, diminished, augmented, played in canon, harmonized in multiple ways and put into various voices in various keys.
Such a piece for today's sight-reading exercise is the Chromatic Fugue on BACH by Johann Christian Bach (1735-1782) who was the youngest son of Johann Sebastian. It could be performed equally well on the piano or the organ since it doesn't have any pedal part.
Play this fugue very slowly because it is extremely chromatic. Aim for articulate legato touch. Interestingly, the piece is written in F major, but the cadence on page 3 is in C minor (half authentic cadence). This fugue will challenge your harmonic skills as well because these sequences will take you to some wild keys.