Step 1Heat the butter in a saucepan over medium heat. When hot, add the flour and stir, cooking until the mixture is a pale yellow and the raw flour taste is gone, 2 to 3 minutes.
Step 2Add the milk, a little at a time, stirring constantly. When it is thick and beginning to bubble, about 4 to 5 minutes, add the onions, garlic, nutmeg, cayenne pepper, white pepper, black pepper, paprika, salt and spinach. Cook for 2 or 3 minutes, stirring all the while. Remove the saucepan from the heat and cool the mixture completely.
Step 3Heat the oven to 350 degrees.
Step 4Roll and shape the pastry to fit a 9-inch pie pan. Set aside.
Step 5In a separate bowl, beat the eggs and fold them and the crawfish into the spinach mixture. Pour into the pie shell.
Step 6Bake the pie until the crust is golden and the center of the pie is set, 60 to 70 minutes. Cool 15 minutes before serving.