- Preheat oven to 350°F.
- Grease cookie sheets.
- Beat brown sugar and butter in large mixing bowl until light and fluffy.
- Add egg and vanilla; beat until creamy.
- Stir together flour, baking powder and salt; gradually add to sugar mixture.
- Divide dough in half. Add cocoa to 1/2 dough.
- Wrap in a Saran Wrap and chill before rolling the dough.
- Roll dough separately on floured waxed paper into 2 rectangles, about 1/4-inch thickness.
- Top one with the other and press together with rolling pin.
- Roll up lengthwise, jelly roll fashion.
- Trim edges; wrap and chill.
- When firm, cut roll into 1/4-inch slices and bake on prepared cookie sheets 12-15 minutes.