Preheat your oven to 365°F and line two baking sheets with parchment paper.
In a large bowl, beat the egg whites on high speed until stiff peaks form.
With the mixer running, gradually add the powdered sugar a few tablespoons at a time. Beat until glossy and smooth.
Add the finely ground walnuts, cinnamon, vanilla extract, and salt. Continue beating on low speed for 1–2 minutes until fully combined. Gently fold in the coarsely ground walnuts with a spatula.
Using a cookie scoop, scoop the dough and place the balls onto the prepared baking sheets, spacing them about 1 inch apart.
Bake for 10 minutes. Let cool on the baking sheets for 5–10 minutes before transferring to a wire rack to cool completely.
Video
Notes
Make sure your bowl is completely clean and dry before beating the egg whites.
The cookies will firm up as they cool, so avoid overbaking.
Store in an airtight container at room temperature for up to 4 days.