Peel and boil the potatoes until just tender. When cool enough to handle, slice into 1/4 inch rounds. Set aside.

While potatoes are boiling, slice the eggplants crosswise into 1/2 inch rounds and spread on a baking sheet lined with paper towels. Sprinkle generously with salt on both sides, then top with another baking sheet weighted down (with cans, or a jug of milk - be creative; you just want weight). Set aside 15 minutes, while preheating broiler.

Pat and gently squeeze eggplant slices with paper towel to remove as much moisture as possible. Rinse under running water, and dry once again. Slice zucchini into 1/4 inch rounds. Toss zucchini and eggplant slices on baking sheet with 2 tablespoons of olive oil, then arrange in a single layer. Broil on highest oven rack for 6 minutes, or until slightly charred, then flip slices and repeat on the other side. Set pan aside.

Make meat sauce: Heat the remaining 2 tbsp olive oil in a large saucepan over medium heat. Add onions and cook until softened, then add garlic and cook 1 minute more. Add ground lamb and cook until browned, stirring often and breaking up any large pieces with a metal spoon. Stir in tomato paste and cook 1 minute, then stir in diced tomatoes and red wine, or red wine vinegar. Add the bay leaves, cinnamon sticks, and cloves. Reduce heat to low and simmer, about 30 minutes. Season to taste with salt and pepper.

Make white sauce: Melt butter over moderate heat in a medium saucepan. Stir in flour and cook 1 minute, stirring constantly (the goal is to cook out the starch, but you don't want to brown it - reduce the heat if necessary). Whisk in 1/4 cup of the milk until fully blended, then very gradually whisk in remaining milk. Stir frequently until sauce is thickened. Slowly sprinkle in cheese and stir to combine. Season to taste with salt and nutmeg. Reduce heat to minimum, and continue to stir now and then while you assemble the moussaka.

Assemble the moussaka: Preheat the oven to 350 degrees. In a large baking dish, arrange a bottom layer of overlapping eggplant and zucchini slices (alternating). Spread the meat sauce over top. Add another overlapping layer of eggplant/zucchini, followed by the potato slices. Pour the white sauce over top and bake for 45 minutes to 1 hour, until bubbly and browned.