Preheat the oven to 400 degrees F and adjust the rack to the middle position. Place the potatoes, sausage, and shallots on a large sheet pan lined with unbleached parchment paper. Drizzle the sausage mixture with the ghee and season with the sea salt. Toss to coat the vegetables and meat with the fat. Roast for 30-40 minutes, until edges of potatoes are turning golden brown.
Sprinkle the 4 cups of spinach over the hot sausage mixture. Sprinkle with the lemon juice and then toss to incorporate. You can serve alone or with a dollop of mayo.