Heat oven to 350. Beat together brown sugar, peanut butter and butter, until light and fluffy. Blend in water, egg and vanilla; add combined dry ingredients; mix well. Shape dough into 3 cm balls. Place on ungreased cookie sheet; flatten to 1 cm thickenss with bottom of glass dipped in sugar. Bake 8 10 minutes or until edges are golden brown. Remove to wire rack, cook completely.
In a heavy saucepan over low heat, melt chocolate pieces and vegetable shortening; stir until mixture is melted and smooth. Top each cookie with half teaspoon melted chocolate; sprinkle with chopped nuts. Chill until set. Store in an airtight container. Makes 6 dozen.