01 - 
                Peel and slice the potatoes thinly, by hand or by using a mandoline or food processor.
              
              
              
                02 - 
                Use a little of the butter to grease a dish around 30 x 20 x 5cm (about 12 x 8 x 2 inches).
              
              
              
                03 - 
                Arrange about a third of the potatoes in the bottom of the dish and pour over a third of the hot stock. Sprinkle over half of the onions, herbs if using and season with salt and pepper.
              
              
              
                04 - 
                Add the next third of potatoes and stock, the remaining onions, some herbs and seasoning.
              
              
              
                05 - 
                Finish with the last of the potatoes, stock and seasoning.
              
              
              
                06 - 
                Divide the butter into pieces and dot over the potatoes. Bake for an hour at 200°C, 400°F, 180°C fan or Gas 6.
              
              
              
                07 - 
                Remove from the oven and let stand for a few minutes before serving.