Mix the dressing ingredients together then keep to one side. Remove the Black Pudding outer skin & then slice into 6 rounds. Heat a non-stick frying pan over high heat, then add a few drops of rapeseed oil. Once the pan is very hot add the potatoes, apple & black pudding & fry on both sides until rich & caramelised. Next add the shallot, garlic and butter, reduce heat to medium & cook for 2 minutes carefully mixing through the pan. Season to taste then divide between two warm plates. Toss the watercress in the dressing and scatter over the plates, drizzling a little extra dressing.