1. Wash leeks and slice them into rings discarding roots and green tops.
2. Saute leeks in the butter in a large skillet until they begin to wilt.
3. Then add mushrooms and toss to coat.
4. Combine stock, sugar, saffron and ginger.
5. Pour the liquid over the vegetables.
6. Simmer, covered for about 2 minutes (just long enough to soften the mushrooms a little).
7. Add the flour/butter mixture, stirring rapidly over low heat until the liquid thickens and vegetables are evenly coated.
8. Add salt and pepper to taste.