This sample is made with a left over piece of the quilted side of the original bag. It has the top layer, a batting layer, and a backing. Handles work best if they have substance and flexibility so you need to test the weight of the fabric you're considering as well as the feel. You may find that a layer of interfacing will give you the substance you want.
With the Barbara bag, both the length and the width of the handle was decided by the scraps I had left over from making the bag. They came from the side piece that I had layered and quilted. If you know you want to use the same fabric, it saves time to do them all at once. If you prefer a certain size of handle, you'll cut the strip roughly double as it's folded in half lengthwise. I prefer to prepare the fabric first and then cut to size to ensure accuracy.
To start, curve all four corners of the handle using an appropriately sized circle. Above, I've used the inside core of a roll of tape. To make sure the corners are roughly the same size and shape, I trace one corner, fold the fabric width-wise to match the parallel corner, and cut through both layers of fabric and then I fold in the strip length-wise and cut the two remaining corners. Curves make it easier to apply the bias tape.
The resulting piece has a long oval shape. Bias tape is pinned right sides together with the handle fabric and then stitched in place. The width of the bias needs to be enough to fold to the back and extend beyond the stitching line. The width of the seam is equal to the finished width you would like that decorative edge to have. Mine are typically about 1/4".
Once the bias tape is stitched in place, press it over to the wrong side being very careful at the curved edges. They will want to pull in and narrow and you'll want to gently ease them so that the width of the bias is equal all the way around. This is why you use bias tape - to go around the corners nicely. I prefer to make my own rather than use purchased tape.
One the bias is pressed to the back, stitch it in place by first stitching in the ditch and then stitch again about 1/8" away. The first line of stitching acts as a cutting guide and the second one works to doubly secure the bias to the handle. On the back, use sharp scissors to trim away the excess bias fabric. I've used contrasting thread in the sample so that you can see it clearly. It would be best to use thread that matches or blends.
From the right side, you will see the bias edge which should be roughly even all the way around as well as one top-stitch-ish line of thread and one that is in the ditch. With matching or blending thread these will not be as visible as they are in my sample.
Next, use a zigzag stitch to stitch over the two lines of stitching working back and forth from the ditch toward the outer edge and onto the bias tape. If you want a densely, satin-stitched line of stitching, go around the handle once with a longer spaced zigzag and then again with a narrower spaced one until you get the density you're looking for. If you want a less dense line of decorative stitching, make some samples first to determine the look you'd like and then work around the piece once.
The reverse side will end up nearly as finished looking as the front side. In my sample, you can see bits of white thread showing beside the zigzag stitching. This is because the width of my stitch was barely enough to cover the two lines of stitching and where they were not completely parallel, it didn't cover. With matching or blending thread this wouldn't be as much of an issue but the width of the stitch is something you might want to test first. If you're doing two rows of zigzag stitching, the first row acts as a test.
At this point, I would stitch the curved edges of the handle to the bag before folding it in half lengthwise because it's both easier that way and it ensures that the open edge is long enough to do the job of securely holding up the bag. After stitching the curved edges, I fold the length of the handle in half and stitch it together. If you want an even firmer handle, you could insert cording into the fold.
The sample handle is quite wide. The initial strip was 2 1/2". If I was inserting cording, I might need that width for the curve of the cord. Without it, I'd chose a narrower initial width. Again, that's something you'll have to play with to get your preferred size.
Hope that helps.
Talk soon - Myrna
Grateful - possibilities