Beat butter, sugar and vanilla in bowl until smooth and creamy, 3 minutes. Mix flour, cocoa and salt in small bowl. On low speed, beat into butter mixture. Add walnuts; beat until blended. Chill 1 hour or until firm enough to handle.
Heat oven to 375°F. Roll dough into balls, 1 tablespoon each. Press unwrapped Kisses in centers. Place on ungreased baking sheet, spacing 1/2 inch apart.
Bake in 375°F oven 10 to 12 minutes, until set. Cool slightly on sheet on rack. Remove cookies to rack to cool. Dust with confectioners sugar. If desired, dust with sugar again before serving.