Soak porcini in 300ml hot water for 30 minutes.
Preheat the oven to 180°C / 350°F / Gas mark 4.
In a pan large enough to hold the chicken in one layer brown both sides. Or do this step in batches.
Squeeze lemon juice over the chicken and transfer to a casserole dish and set aside.
Melt the butter in a medium pan.
When it stops foaming, add the onion and 1 teaspoon of salt, then sauté until it turns light gold.
Meanwhile, remove the porcini from the water and rinse well. Pat dry and finely chop.
Strain the water through a sieve, and retain the mushroom water.
Add the porcini and pumpkin pieces to the onion and sauté for 5 minutes.
Add the chestnut mushrooms and cook for 5 minutes more, stirring frequently.
Stir in the cream, 4-5 tablespoons of the porcini water and season with salt and pepper if necessary.
Simmer uncovered for 10-12 minutes until reduced slightly, then pour over the chicken.
Cover and cook in the oven for 30-40 minutes, turning the chicken once adding a few tablespoons of the mushroom water if the sauce becomes a little dry.
Use tap water if you don’t have any of the mushroom water.
Allow to cool fully before placing foil over and putting into the fridge until the next day.
Serve in the cooking dish for appearance, dotted with a few fresh sage leaves if using and serve directly to guests at the table.