1. In a small bowl, whisk together egg replacer with 2 tablespoons rice milk; set aside. In a medium bowl, whisk together oat and barley flours, salt, and baking powder; set aside. In the bowl of an electric mixer fitted with a paddle attachment, cream shortening and sugar until blended. Add egg substitute mixture, vanilla extract, and remaining 1 tablespoon rice milk; mix until incorporated. Add dry ingredients; mix until just combined, scraping down the sides of the bowl with a rubber spatula if necessary.

2. On a work surface, gather dough and form into a disk. Wrap in plastic, and refrigerate for at least 1 hour.

3. Preheat oven to 375 degrees. Place chilled dough on a lightly floured work surface; if dough seems dry, sprinkle with a few drops of water and knead gently to work in. Using a lightly floured rolling pin, roll out dough to 1/4-inch thickness. Using 3-inch alphabet cookie cutters, cut out desired shapes. Firmly press currants, chocolate chips, or coconut flakes onto cookies, if desired. Transfer to a baking sheet lined with parchment paper or a nonstick baking mat; bake for 8 minutes. Transfer sheet to a wire rack to cool; let cool completely on sheet before removing.