Soak the mushrooms in the water for 30 minutes to reconstitute. Agitate the mushrooms to remove any debris, then remove the mushrooms, strain the liquid through a chinois or fine cheesecloth and recombine the two.
Combine the mushrooms and their liquid, the salt and sugar in a small sauce pot and bring the mixture to a simmer. Cook the mixture until the color changes to light amber, then remove from the heat, add the brandy and ignite, then allow the flames to die off.
Remove the pan from the heat, then add the cream and whisk to incorporate.
If the sauce seems to thin, reduce a bit more, whisking occasionally until thickened to your liking. If it’s too thick, add a tablespoon of water at a time to loosen it. The sauce will keep for months in the fridge, but if it’s around for that long there’s something wrong with you.