Melt the butter and fry the onions and garlic until soft.
Add the mushrooms, stir, add the wine, season, and cook until very soft.
Drain the liquor from the mushrooms, reserving the mushrooms and onions, into another pan, and then reduce this liquid to a thick syrupy texture.
Pass the mushrooms through a food mill or chop finely, then add back to the thick liquor.
Add the herbs and nutmeg. The consistency should be firm.
Taste and adjust the seasoning if necessary.
Serve on top of crostini, slices of baguette or toast.
