Heat oven to 325°. Coat a baking sheet with vegetable spray or line baking sheet with parchment paper.
In a large bowl, beat egg whites until foamy. Gradually add sugar and continue to beat until glossy stiff peaks form, about 4 minutes.
Add cooled chocolate, pecans and vanilla, mixing until incorporated.
Drop tablespoonfuls of mixture onto prepared baking sheet, 2 inches apart.
Bake at 325° for 12 minutes, until set. Cool on baking sheet 2 minutes. Transfer cookies to a wire rack to cool completely.