Ingredients
40g porcini mushrooms  
30g butter 
2 tsp oil 
1kg bag of onions, peeled and thinly sliced 
4 cloves garlic, finely chopped or minced 
½ tsp sugar 
4 tsp salt 
150g king oyster mushrooms, cut into half and then.  Slices 
150g portobello mushrooms, cut into halves then chunks 
250g chestnut mushrooms, cut into halves then chunks 
200g baby mushrooms, cut in half 
250g cooked puy lentils 
½ tsp white pepper 
250ml vegetable stock 
1 tbsps Worcestershire sauce black pepper  
1 kg potatoes, I like Vivaldi’s 

Method
Preheat the oven to 180c. 

In a frying pan put 30g of the butter and 1 tsp of oil and when the butter has melted, put the onions in the pan, put ½ tsp salt over the top and cook for 25-30 mins until soft and going golden.  At this point the onions will look like a lot but they will break down to a quarter of the volume. When you think they are done, add the garlic, sugar, ¼ tsp salt, give it a good stir and cook for a further minute or two. 

Once the onions are cooked, tip into a bowl and put to one side.  Put the marsala into the pan and scrape the bottom, cook until the liquid has reduced by half then tip on to the onions. 

Reduce the heat to medium and put 1 tbsp and 10g of butter into the pot, once melted, add all of the onions, ½ tsp of salt and the white pepper.  Stir the mushrooms from time to time.  When the mushrooms have shrunk by roughly half, increase to medium high and cook until the liquid has gone.  Expect this step to take 15-20 minutes. 

Add the puy lentils to the pot and stir through.  Add the porcini mushrooms and onions along with 50ml of the porcini liquid (being careful to not get any of the grit).  Stir and add the Worcestershire sauce, ½ tsp salt, some freshly ground black pepper and the stock and give everything a good stir.  Check the seasoning. 

Peel and either finely slice the potatoes or use a mandolin to cut them very thinly (2mm).  Put the potatoes into a bag and seal and cook for 5 minutes in your microwave on high.  Very carefully remove the potatoes from the bag and layer them around the edge of the pot, slightly overlapping each other and then in the middle and keep stacking until the potatoes are all used up.  Season the top either with potato spice or the remaining salt.

Cover and put into the oven and cook for an hour.   

After an hour, increase the oven temperature to 200c, remove the lid or the foil and bake for a further 30 mins until the potatoes are cooked and golden brown.