With right sides facing, pin bias tape to neckline, starting at right shoulder. Keep edges of neckline and bias tape matching.

At the center of the 'V' neck, pin the bias tape. Next, fold the bias tape to the left over the pin. 

Fold a second time, creating a 3/8 inch (9mm) fold of bias tape at the top and tapering to a point at the bottom. Reposition the center pin to secure fold to dress.

Adjust bias tape to follow the angle of the neckline and continue pinning up to the left shoulder and across the back.

Return to right shoulder and cut bias tape, leaving 1/2 inch (12 mm). Join bias tape by keeping two ends close to dress. Fold and make a pinch crease.

Pin and sew ends of bias tape together. Take care to not catch dress fabric while joining ends, you can undo pins and move fabric away while sewing, then repin. Trim to 1/4 inch (6 mm) of seam and press open.

Sew bias tape to dress, following fold line, using 1/4 inch (6 mm) seam allowance.

Carefully sew over bias tape fold and stop at pin marking the center neck. With needle in the down position, lift the presser foot and pivot dress to follow angle of the v-neck. Replace presser foot and sew remainder of the neckline.

Fold bias tape over to wrong side of dress, with approximately 1/2 inch (12 mm) of bias tape showing. Open the fold slightly and center the point at the seam. Press and pin in position.

Topstitch along neckline. If your top and bobbin threads are balanced, you can sew the bias tape on the inside.

Press neckline and admire your work.