Heat chocolate and butter in medium heatproof bowl set over saucepan of barely simmering water until melted (bowl shoud not touch water), stirring occasionally. Remove bowl from saucepan; cool to room temperature.
Whisk flour, cocoa, baking powder and 1/4 teaspoon salt in medium bowl. Beat eggs, sugar and vanilla in large bowl at medium speed 1 minute or until smooth and lightened in color. At low speed, beat in melted chocolate mixture until blended. Stir in flour mixture until blended. Cover and refrigerate dough overnight. (Dough will be extremely soft before refrigerating).
Heat oven to 325 degrees F. Line baking sheets with parchment paper.
Place powered sugar in small bowl. Roll 1 tablespoon dough per cookie between hands into 1 inch ball (spray hands with cooking spray to avoid sticking). Roll each ball in powdered sugar. Place 3 inches apart on baking sheets.
Bake 10 minutes or until tops are puffed and crinkled and feel firm when lightly touched. Remove from oven. Place 1 Kiss on top of each cookie; press very lightly into cookie. Bake 5 to 15 seconds or until chocolate just starts to look shiny (soft but not melted).
Remove from oven; sprinkle Kisses with course salt (be generous). Cool on baking sheet on wire rack 1 minute. Carefully place cookies on rack; cool completely (Kisses will be very soft and may lose shape if not careful when moving).