Boil the heerenbone in unsalted water for approximately 40 minutes until completely tender, then drain. Puree the cooked beans with the butter, olive oil, lemon juice and salt in a food processor until completely smooth.
For the Mussels
In a large pot, heat the remaining olive oil to smoking point. Add the mussels all at once and cover with a lid. Cook for a minute, then lift the lid and stir to evenly distribute heat. Add the white wine, cover and cook a further two minutes until all the shells have opened. Strain, retaining the mussel stock. Remove the cooked mussels from their shells – make doubly sure all beards are removed.
Heat the mussels in a little bit of their own stock. Add the remaining stock to the heerenbone puree and heat through. Flash fry the dune spinach leaves in a bit of olive oil and a squeeze of fresh lemon juice. Scoop the puree into heated bowls, top with mussels and dune spinach leaves and serve.
* Heerenbone (English translation: “The Lord’s bean”): This South African heirloom bean is still cultivated in the Sandveld area of the west coast of South Africa. Substitute with butter beans or lima beans.
** Dune spinach is a native plant indigenous to the dunes of South Africa. Substitute with baby spinach or New Zealand spinach.