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You can't print in white at home, and I'd pick different fonts and pattern for the inside paper, but the basic idea of this would be easy. Print two sided, cut, fold. Add some sort of embellishment on the bottom edge. She has the lace detail here, but you could even do some twine to fit with your whole burlap/rustic feel, and a pretty herbal/earthy printed paper to line the envelope.
fun for a child or anyone: punch holes in simple gift wraping

Baba Souk