First, cut out two rectangles of fabric and backing. One 36x15cm and one 10x6cm.
Iron the backing to the back of the fabric. While you are at it, fold the big rectangle lengthwise with the back outside. Iron it flat. Fold the small rectangle lengthwise with the right side out. Then fold the two "wings" again lengthwise. Iron it flat and sew along the edge.
Sew along the edge of the folded large rectangle with 1cm allowance. Leave one of the sides open.
Cut away the allowance on two sides.
Turn i inside out and iron it.
Turn the fabric on the open side to form a "lip".
Sew it shut close to the edge.
Fold the piece into a "Z".
Lay it flat
Fold it lengthwise and sew a bout 1cm away from the fold about 1 cm length.
Fold the two long sides towards the middle and hold it like this:
Looks like a bow tie already... Secure it in place with a little stitching in the middle.
Now, take the small long rectangle you prepared earlier and hold its end against the back of thew bow. Wrap it around the middle, cut the overstanding part off (or fold it in) and sew it to form a ring.
Now you can put an elastic band through the ring to put the bow tie on. Or use a clip. Or sew a nicer ribbon with the same fabric.