HEAT oven to 375°F.
MIX first 5 ingredients until blended. Beat butter, sugars and peanut butter in large bowl with mixer until light and fluffy. Add egg and vanilla; mix well. Gradually add flour mixture, mixing well after each addition. Stir in chocolate.
DROP heaping tablespoonfuls of dough, 2 inches apart, onto baking sheets.
BAKE 10 to 12 min. or until lightly browned. Cool 1 min. on baking sheet; remove to wire racks. Cool completely.