First you will need a onesie (I used a collared one instead of the standard envelope sleeve kind), a washcloth, and a bib to use as a template.
Next turn the onesie inside out and cut along the side seams.
Then cut out the collar.
Cut off the sleeves.
Split the back off the collar.
Use your template bib to cut out the shape.
Cut out the onesie snaps.
Cut out the washcloth for the back. This one isn't quite big enough to cover the whole back so I made patches.
Cut and sew patches from the washcloth. Make sure to measure the bib on your baby, and shorten it if necessary. When I checked this one on Bubba it was longer than I expected, and it hung way down on his chest like a necklace.
Pin the washcloth and onesie inside out, and sew.
Turn right side out and hand sew snaps.
Turn in the edges of the collar and hand sew.