I have been using dried mushrooms and tomatoes since the late early 80’s when I worked at a French Restaurant in Boca Raton. The recipes at this Mobile 5 star establishment were very authentic. Many of the recipes called for fresh morels and chanterelles but the produce in this part of the country at that time was far from great: forget getting fresh exotic mushrooms. The chef ordered all of the dried specialty mushrooms from France and we would carefully clean and re-hydrate these wonderfully earthy mushrooms to use in our dishes.
Once I have re-hydrated the mushroom or tomatoes I reserve the liquid and almost always use it in the recipe I am making with the mushrooms or tomatoes. The liquid from dried porcini mushrooms is absolutely the best when used in a sauce. The flavor is intense and delicious.
Place the dried mushrooms/tomatoes in a saucepan and cover with water by about ½ inch. Bring the mixture to a rapid boil. Remove the pan from the heat and let step for at least 30 minutes. Strain the mushrooms/tomatoes over a bowl through a fine mesh strainer lined with a paper towel or coffee filter. Let the liquid drip through completely. Rinse the mushrooms/tomatoes under running water and gently squeeze the liquid out of the mushrooms/tomatoes over the strainer into the bowl. Re-strain the liquid a second time in the same manner as the first. Use this liquid in your recipe where water or stock is called for. The mushrooms can be used as is or chopped and cooked with other mushrooms in the recipe. The tomatoes are generally chopped before using. Your recipe will tell you what to do.