Preheat oven to 325°.
Place 1/4 cup sugar in a small bowl. Scrape seeds from vanilla bean, and add seeds to sugar; discard bean. Stir well with a whisk.
Beat egg whites, cream of tartar, and salt at high speed of a mixer until foamy. Gradually add 3/4 cup sugar, 1 tablespoon at a time, beating mixture until stiff peaks form. Gradually add vanilla bean mixture and extract; beat until just combined. (Stiff peaks will take on the consistency of marshmallow cream.)
Cover a baking sheet with parchment paper; secure to baking sheet with masking tape. Drop batter by level tablespoonfuls onto prepared baking sheet. Bake at 325° for 35 minutes or until crisp. Cool on pan on a wire rack. Repeat procedure with remaining batter, reusing parchment paper. Store in an airtight container.
Add the vanilla bean seeds at the end of the beating process, as their natural oils can prevent the egg white from beating to stiff peaks. When baked long and slowly, stiffly beaten egg whites turn crisp, as they do in these cookies. Bake them 10 minutes less for a cookie that's slightly chewy on the inside. Store cookies in an airtight container for up to a week or freeze for up to three months.