- Preheat oven to 350 degrees. Fill a 4-quart saucepan with 3 quarts water and ½ cup of salt and place on stove over high heat. Meanwhile, peel parsnips on a cutting board and trim into approximately 3-inch long pieces. (Since parsnips have a conical shape, the thin side of the taper will end up being one single piece, while the wide top side will be sliced into multiple pieces, mimicking the thickness of the single piece from the bottom.) Prepare a bowl of water with lots of ice and set aside. When water reaches a boil, add parsnips to boiling water and let cook for 2 to 3 minutes or until the starches begin to release and form some foam across the top of boiling water. Using a slotted spoon, remove par-cooked parsnips and transfer to the bowl of ice water. Let sit until they stop carry-over cooking, about 2 minutes. Using a slotted spoon, first remove the ice from the bowl, then remove the parsnips and place them on a kitchen towel to absorb any excess moisture. Reserve the bowl of water to wash the leek in next step.
- Place leek on a cutting board, and trim away the woody dark green tops and hairy root and discard them. Cut in half crosswise, then cut each section in half lengthwise. Slice the leek sections crosswise into 1/8-inch strips. Transfer sliced leeks to bowl of water and move them around in a rapid circular motion, separating any any clinging pieces to remove any hidden dirt or sand. The leeks pieces will float to the top and dirt or sand will sink to bottom. With a slotted spoon, remove leek pieces, taking care not to stir up the dirt or sand at the bottom of bowl. Place on a kitchen towel and blot dry.
- Choose a pan that will hold parsnips snugly, like a small casserole dish or loaf pan. Arrange half of the leeks on bottom of pan and then place all of the blanched parsnips across leeks. Add remaining leeks to pan. Season with remaining teaspoon of salt, pepper, and nutmeg, then add cream. Place dish on a small sheet pan (to catch any cream that may spill over the edge of dish while cooking) and place the pan on center rack in oven. Cook for 35 to 40 minutes, until cream thickens slightly and leeks and parsnips are lightly browned in places. Taste for seasoning and serve hot.