MELT 1 cup morsels in a small, heavy-duty saucepan over lowest possible heat. When morsels begin to melt, remove from heat; stir. Return to heat for a few seconds at a time, stirring until smooth. Cool to room temperature.
COMBINE flour, baking powder and salt in a small bowl. Beat sugar, margarine and vanilla extract in a large mixing bowl. Beat in melted chocolate and egg whites. Gradually beat in flour mixture alternately with water. Stir in remaining morsels. Cover; chill until firm.
SHAPE dough into 1 1/2-inch balls; roll in powdered sugar to coat generously. Place on greased baking sheets.
BAKE in preheated 350° F oven for 10 to 15 minutes or until edges are set but centers are still slightly soft. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.