This incredibly fun and mostly kick ass harpsichord cadenza is from the 1st movement of Bach’s Bradenburg Concerto No.5. Some info according to Wikipedia:
This concerto makes use of a popular chamber music ensemble of the time (flute, violin, and harpsichord). It is believed that it was written in 1719, to show off a new harpsichord by Michael Mietke which Bach had brought back from Berlin for the Cöthen court. It is also thought that Bach wrote it for a competition at Dresden with the French composer and organist Louis Marchand; in the central movement, Bach uses one of Marchand’s themes. Marchand fled before the competition could take place, apparently scared off in the face of Bach’s great reputation of virtuosity and improvisation.
The concerto is well suited throughout to showing off the qualities of a fine harpsichord and the virtuosity of its player, but especially in the lengthy solo ‘cadenza‘ to the first movement. It seems almost certain that Bach, considered a great organ and harpsichord virtuoso, was the harpsichord soloist at the premiere. Scholars have seen in this work the origins of the solo keyboard concerto; indeed it is said to be the first-ever example.
This excerpt is from Trevor Pinnock and the English Concerto Orchestra cd.
Download Audio: Brandenburg Concerto No.5 mv 1[audio:bc5.mp3]