Melt 3 tablespoons of butter in a skillet over medium-low heat. Add scallions and parsley; cook and stir constantly until scallions soften, about 2 minutes. Stir in spinach and cover; cook until spinach starts to wilt, about 5 minutes. Uncover and continue to cook, stirring occasionally until flavors combine, about 20 minutes.
Beat eggs with an electric mixer in a large bowl until thick and light in color. Beat the spinach mixture into the eggs; add salt and ground black pepper.
Melt remaining butter in a heavy 10-inch skillet over medium heat; pour in the egg mixture. Cover and cook until eggs are set, about 10 minutes. Loosen the edges of the pancake with a spatula; turn out onto a serving platter. Cut in two with a sharp knife.