Take all ingredients for the butter and mix them until smooth (one cup = 200 ml).
Put the butter in the baking pan (not to small and shallow!) and sprinkle with chopped walnuts. Bake it 30 minutes at a 200 degrees Celsius.
When it's baked (try with the toothpick - don't wait for it to come out entirely dry), take it out and carefully cut in squares. Do not put the knife all the way down.
While the butter is in the oven and almost done, make the frosting (it's more like a glaze, really):
Put sugar and water in the small sauce pan and let it boil for a few minutes, almost to form a syrup (not thick!). Remove from the heat and add chocolate and margarine. (You can add more than 100 grams of chocolate if you want.) Mix with the spoon, until smooth. Then mix in the oil.
Pour while still warm over the hot brownies.
If you want coconut, and not the walnuts, do not sprinkle them before the baking, but after, over the moist glaze.
After it cools down a little, put it in the fridge. It's ready to use after 2-3 hours.