Complex sentence: The very first Bisto product, in 1908, was a meat flavoured gravy powder, which rapidly became a bestseller in the UK as it was added to customers' own gravies to give a distinct rich taste and aroma.
Split into simpler sentences: The very first Bisto product, in 1908, was a meat-flavoured gravy powder, which rapidly became a bestseller in the UK. It was added to customers' own gravies to give a richer taste and aroma.