Heat the oil in a wide non-stick frying pan. Add the garlic and sage. Season the celeriac slices, fry in batches for approx. 10 mins. on each side. Pour in the stock, add the bay leaf, cover and cook for approx. 5 mins. Add the beans, continue to cook for a further 5 mins.
Combine the mustard, balsamic and oil. Add the olives, capers, parsley, lemon zest and juice, mix and season with salt. Plate up the celeriac steaks and beans in deep dishes along with the stock, drizzle the olive salsa on top.