Puree 300g cooked chestnuts, 3/4 cup tahini paste, 2 large garlic cloves, 3/4 to 1 cup water, the juice of 1 lemon, 1/2 cup olive oil, and 1 teaspoon cumin in a food processor or blender until smooth.
If too thick, just add more water until you have a consistency you like.
Season to taste with sea salt and freshly cracked black pepper.
Place in a serving bowl. Top with a drizzle of olive oil, sumac and chopped parsley. Serve with a platter of crunchy vegetables at a dinner party or it can be used instead of butter as a spread on bread or toast.
It can be stored in the fridge for up to seven days.