Cut the mushrooms onto pieces - the size depends on your preference and what you intend to use them for.

Heat a large frying pan (I use a cast-iron skillet) over medium high heat and cook the mushrooms in a single layer, without any fat, until they are browned on all the major surface areas. Turn them as necessary to achieve this. Do not crowd the pan, or else it will become swamped with water and the mushrooms will stew in their juices instead. You will need to work in batches. If it looks like there's too much water in the pan, turn up the heat. The liquid should leave the mushrooms and caramelise on the pan almost immediately, but be careful not to burn either the mushrooms or the residue that is left in the pan.

When you have finished, turn off the heat, set the mushrooms aside and add some water to the pan. Scrape up all the mushroom residue. If you have successfully avoided burning the lovely, caramelised mushroom juices as you cook, you will be left with a beautiful, dark, rich mushroom broth. If you have an absolutely huge quantity of mushrooms to sauté it may be better to deglaze the pan a couple of times as you cook, as if the dried juices sit in a very hot pan for too long, they will burn. To check if you have avoided burning it, simply taste the stock after. If it is bitter - unlucky! If not, enjoy an incomparably delicious stock!

Freeze the mushrooms and the stock (if not using immediately) in portions - either in freezer bags or in containers.

Cut the mushrooms onto pieces - the size depends on your preference and what you intend to use them for.

Preheat the oven to about 230c. Arrange the mushrooms in a single layer on a baking tray. You may need to use more than one baking tray, depending on how many mushrooms you have. You do not need any fat. Roast until they are browned on all the major surface areas, stirring as necessary to achieve this. Do not crowd the tray, or else it will become swamped with water and the mushrooms will stew in their juices instead. The liquid should leave the mushrooms and caramelise on the pan almost immediately. You are less likely to burn the mushroom residue using this method (as opposed to the stove-top), but the stock that will result is less intense.

When you have finished, remove the tray from the oven, set the mushrooms aside and add some water to the pan. Scrape up all the mushroom residue. If you have successfully avoided burning the lovely, caramelised mushroom juices as you cook, you will be left with a beautiful, dark, rich mushroom broth. To check if you have avoided burning it, simply taste the stock after. If it is bitter - unlucky! If not, enjoy an incomparably delicious stock!