Melt semi-sweet chocolate with butter in a saucepan over low heat, OR in microwave on HIGH for 2 minutes. In a mixing bowl, beat egg with sugars and vanilla till blended. Beat in melted chocolate mixture. Mix in flour, baking soda, baking powder, salt, and sour cream until blended. Stir in chocolate chips. Chill dough for at least 30 minutes to harden and prevent spreading of cookies. Drop by heaping teaspoonful onto ungreased cookie sheets, 5 cm apart. Bake at 180ºC for 10 to dozen minutes. Cool 2 minutes before removing from cookie sheets. Makes about 4 dozen cookies.