Step 1: Preheat oven to 325 degrees. Put egg white and salt in the bowl of an electric mixer fitted with the whisk attachment, and mix on medium-high speed until stiff peaks form.
Step 2: Reduce speed to medium; mix in nuts and sugar, then flour and lemon juice.
Step 3: Using a 1 1/4-inch ice cream scoop, drop dough onto baking sheets lined with parchment paper, spacing 2 inches apart. Bake cookies, rotating sheets halfway through, until edges are golden, 10 to 12 minutes.
Step 4: Let cool on sheets on wire racks. Cookies can be stored between layers of parchment in airtight containers at room temperature up to 3 days.