How to Make It
Heat oven to 350° F. Line two baking sheets with parchment. Whisk together the flour, salt, and nutmeg in a medium bowl; set aside.
In a separate bowl, beat the butter, brown sugar, cashew butter, and granulated sugar with an electric mixer, on medium-high until fluffy, 2 to 3 minutes. Beat in the egg yolk and vanilla. Reduce speed to low and gradually add the flour mixture, mixing just until combined (do not overmix).
Whisk the egg white with 2 tablespoons water until frothy in a small bowl. Place the chopped cashews in a separate bowl.
Roll level tablespoonfuls of the dough into balls. Roll each ball in the egg white mixture and then in the chopped cashews; place on the prepared baking sheets, spacing them 2 inches apart. Gently make a well in the center of each cookie with your thumb.
Bake, in batches, until lightly golden, 8 to 10 minutes. Cool slightly, then spoon ¼ teaspoon of the apricot jam into each well. Transfer to a wire rack to cool completely.
Storage suggestion: Layer the cookies between sheets of wax paper or parchment and keep at room temperature in an airtight container for up to 4 days.