Sweet and Russet Potatoes Gratin with Sour Cherry Stuffing

If you can n0t decide between sweet or savory potatoes for your next dinner, then I would recommend this dish is for you. These baked mashed potatoes combine sweet, savory and sour flavors into unique dish.Sweet and Russet Potato Gratin with Sour Cherry Stuffing serves 62       large russet potatoes2       large sweet potatoes1/2   cup olive oil1       red onions, thinly sliced1       cup dried sour cherries1/2   cup coarsely chopped walnuts4      cloves garlic, mashed1/4   cup lemon juice1/4   cup orange juice1       teaspoon turmeric1/2   teaspoon chili powder1/2   teaspoon Mediterranean Sumaczest of one lemonszest of one orangefresh gingersalt to taste Peel russet potatoes, cut in halves and then place in heavy pot.  Cover with water and season with salt and turmeric.  Bring to boil and simmer until the potatoes are soft and ready to be mashed. Place the cooked potatoes in a bowl.  Save the cooking liquid.  Mash the potatoes, add lemon zest, lemon juice, grated fresh ginger, 2 tablespoons olive oil and salt.  Add little of the cooking liquid if the potatoes little dry.  Spread the mashed potatoes at the bottom of baking dish.To make the stuffing: saute onions in rest of the olive oil until transparent.  Add the sour cherry, the crushed walnuts, the chili pepper, the garlic and salt.  Spoon this stuffing over the mashed potatoes.Now, boil the sweet potatoes in water until they are soft.  Remove from the water, drain the water, peel the sweet potatoes and place them in a bowl.  Mash the potatoes, add the orange zest, the orange juice, freshly grated ginger, and salt.  Spread the mashed sweet potatoes over the cherry stuffing.Bake the mashed potatoes in the oven, take out of the oven, sprinkle with sumac and serve.