Step 1

Cook, bake, or microwave the potatoes in their skins until just tender. When cool enough to handle, peel and cut into 1/4-inch-thick slices.

Step 2

Cover the cashews with 1 cup of boiling water in a heatproof bowl and let stand for at least 15 minutes.

Step 3

Drain the cashews, then combine with the avocado and lemon juice in a food processor. Process until smoothly pureed; drizzle enough water through the feed tube while the processor is running to give the mixture a thick, creamy texture.

Step 4

Preheat the oven to 350º F.

Step 5

Heat the oil in a large skillet. Add the leeks and sauté over medium-low heat until golden. Add the spinach in batches, covering and cooking until wilted to make room for all of it.

Step 6

Stir in the cashew cream, dill, and matzo meal. Season with salt and pepper.

Step 7

Break each matzo in half, and place in a shallow container. Cover with room-temperature water in a shallow container until slightly pliable (don’t let them get mushy!), about 2 minutes; drain. Lightly oil a 9- by 13-inch casserole dish.

Step 8

Layer the casserole as follows: line the bottom with a layer of matzos, using two matzos per layer. Follow with a layer of potato slices, half of the spinach mixture, half of the optional cheese, and another layer of matzos. Repeat, ending with a layer of matzo and the remaining cheese.

Step 9

Bake for 30 to 40 minutes, or until top is golden with spots of brown. Let stand for 10 minutes, then cut into squares to serve.