This is a very basic project, in that it does not take a lot of time, but it has whimsy and a lot of potential for creative interpretation. Just change up the materials and you could make it funky, out of recyclables, or masculine.
I cut some cardstock in the same size, which you do not have to do. Consider making the width the same and varying length.
Imagine your recipient opening the envelope to find this unique folding letter!