Preheat oven to 350°F and grease a 15x10 baking pan with a bit of butter. Set aside.
In a large mixing bowl, using an electric mixer, beat the shortening and butter for 1 minute on medium speed.
Add the sugar, baking powder, and salt. Beat together until thoroughly combined and mixture is smooth.
Add the eggs and vanilla, and beat until well combined, scraping down the sides of the bowl as needed.
Add the flour one cup at a time, mixing with the electric beater until the dough gets thick. Then, switch to a wooden spoon and stir in any remaining flour.
Reserve 1½ cups of the dough, and press the remaining dough into the prepared baking pan.
Bake for 12 minutes, then remove from oven.
Spread the cherry pie filling over the crust, then spoon small amounts of the reserved dough over the top.
Bake for 25 to 28 minutes longer, or until lightly golden brown.
Remove from oven and set on a wire rack to cool completely.
While the bars cool, prepare the icing by combining the powdered sugar, vanilla extract, and milk in a small bowl, adding the milk 1 tablespoon at a time until desired thickness is achieved.
Once bars have completely cooled, drizzle with icing, cut, and serve.