In a bowl, whisk the egg white until thick and frothy. Add the sugar, ras el hanout and salt and stir to combine. Add the cashews, pecans, pistachios and walnuts and stir to coat with the egg white mixture.
Using a slotted spoon, transfer the nuts to two baking sheets. Bake until golden brown and crunchy, 25 to 30 minutes, stirring halfway. Cool and store in an airtight container for up to two weeks.