1. Cut two squares (matching or not!) 7 3/4'' by 7 3/4''
2. Apply medium weight interfacing to one of the squares. I save my scraps just for this.
3. Sew the squares, right sides together, leaving a hole to turn it right side out. Clip the corners.
4. Turn and sew along two opposite sides of your square.
5. Fold the square in half, bringing the seams together. I like the piece with the interfacing on the outside, but I have made them with the interfacing on the inside fabric and it doesn't make much of a difference.
6. Sew the other opposite edges.
7. Stuff with money. I also put in a index card where I write what the envelope is for and how much goes in each month.