Preheat the oven to 180C. Trim the excess leaves off the leeks, keeping only the white part (you can use the leaves for making stock or risotto). Slice this in half lengthways, and rinse well to remove any dirt or grit. Lay the leeks in a single layer in a baking dish. Pour over the white wine, olive oil and enough water to half cover the leeks, then tuck in the bay leaves and sliced garlic cloves. Season well.
Roast in the oven for 30-50 minutes, until the leeks are completely tender to the point of a knife, and slightly crispy on top.
Drain the liquid off the leeks and put in a small pan, setting the dish of leeks aside. Reduce the liquid to around 3 tablespoons, then remove from the heat. Add the red onion, vinegar and sugar, season, and leave for at least 15 minutes, stirring occasionally.
When ready to serve, warm the dish of leeks up for a few minutes in the oven (or you can serve them at room temperature). Spoon over the red onion dressing, sprinkle over the sumac and parsley, and crumble over the goat’s cheese. Finish with a drizzle of olive oil.