I always enjoy looking at all of the advent calendars posted here, so I thought I'd share mine for this year.
I was wanting something that could be used again from year to year, and was inspired by the "special delivery self-mailing note" project found in the
Handmade Hellos book.
Here is a group shot of all the envelopes I made:

Here is the advent calendar on display:

Each envelope is clothes-pinned to a branch that I wrapped in white yarn.
Here is a close-up of one of the envelopes (front and back):

And here is one of the envelopes opened:

Yay!
