In a medium bowl, beat eggs with nutmeg and 1/2 teaspoon salt; add softened matzo, and mix.
Heat 1 tablespoon butter in an 8-inch nonstick skillet over medium heat, swirling to coat; add matzo mixture, and press in gently. Cook until browned on underside, 4 to 6 minutes; carefully invert cake onto a plate. Heat remaining tablespoon butter in skillet, and slide cake back into skillet. Cook until other side is browned, 4 to 6 minutes more.
- Melt half the butter in a large skillet. Add the onions and cook slowly until caramelized, about 20 minutes. Remove the onions. Sauté the mushrooms in the oil and season with salt and pepper; add them to the onions.
- Heat the remaining butter in the skillet. Add the matzo mixture and stir over moderately high heat until the eggs set, about 5 minutes. Sprinkle with the parsley and serve.