Preheat oven to 300ºF. Line 2 baking sheets with parchment paper. Butter parchment paper.
Beat egg whites in large bowl until stiff peaks form. Gradually fold in powdered sugar, almonds, and lemon juice (meringue will deflate and no longer be stiff).
Drop meringue by level tablespoonfuls onto prepared baking sheets about 2” apart. Bake until cookies are pale golden brown around edges, about 25 minutes. Cool completely on baking sheets. Using a spatula, remove cookies. Store in airtight container.