Peel and thinly slice the onions. Peel and thinly slice the garlic. Melt 50g of the butter (save the rest for your other recipes) in a pan over a very low heat. Add the onions and garlic to the pan with a generous pinch of salt and pepper. Pop on a lid. Sweat the onions for 20 mins, stirring occasionally, till soft. If they start to colour too quickly, turn the heat down even more.

While the onions cook, fill and boil your kettle. Pop the dried porcini mushrooms into a small heatproof bowl and cover with boiling water. Leave to soak for 15 mins, then drain and rinse under a cold tap. Shake the porcini mushrooms dry, chop them into small pieces and set aside.

When the onions have cooked for 20 mins, add 1 tbsp demerara sugar and stir well. Fry for 2-3 mins, till the onions turn sticky. Stir in 2 tbsp flour and continue to fry 2-3 mins, scraping the bottom of the pan with a spoon to keep the flour from sticking.

Add the porcini mushrooms to the onions and crumble in the stock cube. Slowly pour in 750ml boiling water, stirring as you pour, till fully combined. Drop in the bay leaf and stir.

Bring the gravy to the boil, then reduce the heat to a simmer. Cook without a lid for about 20 mins, till the liquid has reduced a little and the flavour has intensified. Just before serving, taste the gravy and more salt or pepper if needed. Pour into a jug and serve.