First, wash the dried mushrooms under running water and then soak in 1-2 cups of hot water, cover the vessel and keep aside for 10 minutes. You can either snip the soaked mushrooms under the water or drain them and chop into even sized pieces. Do NOT throw away the water in which they were soaked as it is full of flavour and we will be using it later to build the sauce of the stroganoff.
In a heavy bottomed pan, heat the olive oil. Add the onions, garlic, fresh thyme and marjoram. Saute on medium heat, till they are soft.
Add the chopped fresh and rehydrated mushrooms, stir well to mix with the aromatics. Let this cook on medium flame till nearly done, say 5-7 minutes.
Add the tomato puree and cook it off for 2-3 minutes on high flame.
Add the stock cube, the water in which the mushrooms were soaked. Cover and let this simmer till the mushrooms are soft, for about 5 minutes.
Next, add the brandy, mustard, paprika. Make a slurry of cornstarch in a little cold water and add it to the simmering stroganoff along with the sour cream. Add some water if you think the sauce is drying out. Add salt and let this simmer for 5 minutes until all the flavours infuse into the mushrooms.
The final dish should be a stew of very flavourful mushrooms in a good quantity of thickish sauce that you can eat the rice / spaghetti with.