Cut a 2 inch (5cm) bias strip of fabric and press in half - no folded edges like normal bias
Cut a contrasting fabric strip or in my case lace. If you were using fabric then make your width 2cm wider than the first, again folding in half and pressing. The lace I'm using is only1 inch and is not folded over. It is the same width as my fabric so it is short underneath and won't sit on the fabric edge.
Determine how you want your decorative strips to look
Place both pieces on your right side of fabric aligned with the fabric edge and then cover with the top fabric. Your decorative strips will be sandwiched in between.
Pin to secure
Both strips need to be caught in you seam allowance. I needed to take extra care as my seam allowance just caught the edge of the lace.
Sew your seam
Turn your piece over to the right side and press your strips to one side. Make sure the seam allowance underneath on your right side is underneath the decorative strips so it will get caught when you sew the top stitch keeping them flat.
Sew a top stitch to the outer edge of the strip closest to the seam It will look a bit like a felled seam
Here is what it will look like from the back - normally you would still finish off your edges as need to.
Give your seam a final press