Preheat oven to 375F.
In the bowl of a food processor, add the butter, 1 cup sugar, flour, salt and baking powder. Run the machine until the mixture is homogenous and resembles large crumbs. Add the eggs and pulse until a dough forms.
Line a quarter sheet pan with parchment paper. Take half the dough and press it into the pan. (You may want to cover it with another piece of parchment and using a rolling pin. I did both). Roll out the remaining dough between two pieces of parchment into a rectangle.
In a bowl, stir together the cornstarch and 1 cup sugar. Add the cherries and apples, toss to coat. Spread the fruit mixture over the dough pressed into the sheet pan.
Peel off the top piece of parchment covering the remaining dough rectangle. Flip the dough onto the fruit (dough side down, remaining parchment side up), then carefully peel back the remaining parchment.
Bake for 40 minutes. Remove from oven and cool slightly.
Mix together the powdered sugar, milk and vanilla to make the glaze. It should be thick, but pourable- add small amounts of milk if necessary. Pour over the bars and allow to set. Cut into squares and serve.