Before using the candy, you'll need to crush it up by placing each color you're using in a small, heavy plastic bag and pound it with a mallet or hammer.
Cookies: In a medium mixing bowl beat butter and shortening with an electric mixer on medium to high speed for 30 seconds. Add sugar, baking powder, and salt. Beat until combined, scraping sides of bowl occasionally. Beat in eggs and vanilla until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour with a wooden spoon or use your stand mixer and you will have no issue combining all flour. Cover and chill for one hour or until dough is easy to handle.
Preheat oven to 375. On a lightly floured surface roll a portion of the dough ¼ inch thick. Cut dough using desired shape. Cut out cookie centers with smaller cutter. Place on foil lined cookie sheet and fill center with crushed candy.
Bake for only 10 minutes. Do NOT over bake!!
Transfer to wire rack to cool completely.
Recipe by I'm At Home Baking! at http://imathomebaking.com/stained-glass-cookies/