BEAT first 4 ingredients with mixer until well blended. Add flour and baking soda; mix well. Divide dough in half. Mix half the dough with chocolate. Divide each portion in half again. (You will have 2 white and 2 chocolate pieces.)
ROLL 1 white dough piece into 10x8-inch rectangle on lightly floured surface. Top with 1 chocolate piece, broken into smaller pieces; press gently into white dough. Starting at one long side, tightly roll up dough to form log; wrap with plastic wrap. Repeat with remaining dough. Refrigerate 1 hour.
HEAT oven to 350ºF. Cut each log into 30 slices; place, 2 inches apart, on baking sheets. Bake 10 to 12 min. or until lightly browned. Let stand on baking sheets 2 min.; remove to wire racks. Cool completely.