Make the ricotta white sauce by combining ricotta, grated hard cheese, milk and 1 tablespoon olive oil in a blender; blend until smooth and creamy, adding a little more milk if needed. Season with salt, pepper and nutmeg.
Heat 2 tablespoons olive oil in a large skillet over medium-low heat. Add the minced shallot and the spinach, cover and cook 2 minutes, then remove the lid, stir and cook another 2 minutes until wilted. Remove from heat and set aside.
Preheat the oven to 180°C (350°F) and place a rack in the middle position.
Brush the bottom of a 6x8-inch baking dish with a layer of the ricotta white sauce.
Place a layer of lasagna sheets over the sauce, trimming sheets with a knife so they fit the dish exactly.
Spread half of the pea pesto evenly over the noodles, then top with half of the sliced potatoes, half the sliced mozzarella and half the basil leaves.
Add another layer of lasagna sheets, then spread an even layer of ricotta white sauce over them and top with the sautéed spinach.
Add another layer of lasagna sheets and spread the remaining pea pesto evenly; arrange the remaining sliced potatoes, mozzarella and basil on top.
Finish with a final layer of lasagna sheets and spread the remaining ricotta white sauce all over the top to form a thick white layer.
Bake for about 20 minutes, until the pasta is cooked through and the top is gently bubbling.
For golden spots, place the lasagna under the grill for about 5 minutes more, then remove from the oven and let rest briefly before serving.