I used three layers of thick corrugated cardboard to create the niche, covered it with old book papers (these are sermons from about 1850), added some gesso and colour with paints and a flower stamp and some stars. Thanks to this niche post on the PA blog: I used a star stencil and modelling paste on the tissue in stead of trying to stencil straight on the frame. It always surprises me how the tissue paper "dissapears" when it is burnished with plenty of glue!
After mounting the ATC on scrap card I covered the back with the same papers, paints stamp and stars. I finished my project with some hanging stars (pierced through the frame with a sewing needle, if I had planned well enough, the ends of the threads would be glued under the papers used to cover the back) and a bouquet made with the same PA mini flower that I used on the frame, just trimmed a bit lower and the stem separated from the leaves. I pierced a small hole in the niche with a craft knife blade and stuck the bouquet in place.