Probably different tastes between here in the U.S. and there, however we do a really simple but delicious 'sauce' when grilling steaks...
Simply melt about 1/2 stick of butter in a heavy pan and add about a cup of Worcestershire, salt to taste and, of course, the thickly sliced mushrooms (we like portabellos). Some of our family also like sliced onions, but I'd rather forgo those.
If one wants a little thicker 'sauce', simply add about 1/2 teaspoon of flour stirred into 1/2 cup cold water, added to the mushroom mixture a little at a time. Simmer until the steaks are ready. Let each person add the amount they wish....
Finish with freshly ground pepper to taste...