In a bowl combine butter and dry baking mix. (could add 1 tbsp sugar for sweet filings) Use a fork or pastry cutter to blend so you have a coarse mixture a bit like sand consistency.
Add boiling water and integrate just until you get a ball of dough. You don't want to over-mix as that will make it tough.
Lightly flour cutting board or countertop and flatten dough with palms or rolling pin in a circle so it will fill your pan. Make sure it is same thickness all the way across, but again handle as little as possible for best results.
Lay inside pie pan and gently press to mold into pan and fill with your favorite filling. If you want to add a cold filling this is How to Blind Bake.
Once baked that way, cool, and add cold filling at that time. If baking filling with the crust, leave crust unbaked, pour in filling and follow your directions in regards to how long and at what temp to bake your pie at.