Grate the radishes on a fine grater and place in a bowl lined with kitchen roll (this will absorb any liquid that comes out of the radishes). Beat the butter with a fork until its very soft then add the radishes and combine well with a good twist of black pepper and a generous pinch of sea salt.
Bring a pan of water to a simmer, add the eggs and simmer for 3 mins then put the lid on and turn off the heat, leave to stand for 2 mins.
In the meantime toast the bread and whilst still warm spread generously with the radish butter. Cut the slices into soldiers and serve with the soft-boiled egg.
Notes: Makes a delicious lunch, supper, or breakfast. If you make the butter in advance keep it in the fridge then bring back to room temperature and beat again before spreading.