Step 1Put the potatoes in a medium saucepan with water to cover by about 1 inch and a pinch of salt. Cover and bring to a boil. Simmer over medium-low heat until the potatoes are very tender, about 35 minutes; check by piercing the thickest potato with a fork. Drain and set aside until cool enough to handle. Fill the pan two-thirds full with water and bring again to a boil. Add another pinch of salt.
Step 2Trim the tough ends from the asparagus, and cut the stalks crosswise into one-half-inch pieces. Add the pieces to the boiling water and cook until crisp-tender, about 3 minutes. Remove the asparagus with a slotted spoon (leave the water at a boil), and rinse the pieces under cold water to stop the cooking.
Step 3Add half of the spinach to the pot. Cook quickly, stirring a few times, until the spinach is just wilted, about 1 minute. Remove the spinach with a slotted spoon to a strainer and rinse under cold water, then drain. Add the remaining spinach to the cooking water to blanch, then remove, rinse and drain. Squeeze the spinach dry by the handful, then finely chop. Transfer the spinach to a bowl.
Step 4Chop the leeks and mash the potatoes: Trim the dark green tops from the leeks (discard or save for another use), and halve the leeks lengthwise. Cut the halves crosswise into thin slices about one-fourth-inch thick. Submerge the pieces in water, rubbing them to dislodge any dirt, then drain. While the potatoes are still hot but are cool enough to handle, carefully peel them, then mash them by hand in a large bowl using a potato masher. Set the potatoes aside.
Step 5In a deep sauté pan, heat 2 tablespoons oil over medium-low heat. Add the sliced leeks and season with one-eighth teaspoon each salt and pepper, or to taste. Cover and cook, stirring occasionally, until the leeks are very tender, about 15 minutes. If there is any liquid in the pan, uncover and continue to cook the leeks over medium heat until the liquid is evaporated and the leeks are sizzling. Add the asparagus and heat, stirring occasionally, for 1 to 2 minutes. Taste and adjust the seasoning with one-eighth teaspoon each salt and pepper, or to taste. Remove from heat. Transfer 2 cups of the leek-asparagus mixture to a medium bowl and set aside (this will be added to the potatoes in Step 7).
Step 6Drain any excess liquid from the bowl of spinach. Heat the remaining leek-asparagus mixture in the pan over medium-low heat, adding the garlic and 2 tablespoons of the pine nuts. Add the spinach and heat for 2 minutes, stirring occasionally. Remove from heat and season with one-fourth teaspoon salt, one-eighth teaspoon pepper and one-eighth teaspoon each of the cayenne pepper and nutmeg. Set the mixture aside to cool completely, then add 1 tablespoon dill. Taste again and adjust the seasoning if desired. Fold in 2 of the eggs, one at a time, mixing well after each addition. Add the matzo meal and mix well. Set aside.
Step 7To the potato mixture, add 2 tablespoons olive oil, one-half teaspoon salt, the remaining cayenne, nutmeg and dill, the parsley and the green onion. Add the reserved 2 cups asparagus and leek mixture. Taste and adjust seasoning. Fold in the remaining 3 eggs, mixing well after each addition.
Step 8Heat the oven to 350 degrees. Grease a 2-quart square baking dish with olive oil (the dish should be just large enough to fit squares of matzo). Quickly dip the matzos in a large bowl of water just to soften, then transfer to a towel. Pat the matzo dry.
Step 9Put one matzo inside the baking dish and brush it with 1 1/2 tablespoons olive oil. Top with the spinach mixture. Place the second matzo over the spinach and brush with the remaining 1 1/2 tablespoons olive oil. Spoon over the potato mixture and smooth the top. Sprinkle with the remaining 2 tablespoons pine nuts.
Step 10Bake the pashtidah uncovered until it is firm, about 35 to 40 minutes. Remove from the oven and set aside for 15 to 20 minutes before slicing. Before serving, run a metal spatula or thin knife carefully around the edges. Serve hot or warm.