Here's the deal--if your canned apple pie filling is too soupy, pour off some of it. You can also add lemon juice at this time bc you will want tart and many apples are too sweet for a good pie. Then you add flour to thicken, which compliments the crust also made from flour. I got my pie crust recipe from the Better Homes and Gardens cookbook, before they updated and ruined some of their time-tested favorites. It's just 1:3:5-7 Tblsp.
BASIC PIE CRUST, double layer
1 cup shortening
3 cups flour
1-2 teaspoons salt--taste it
5-7 tablespoons ice water,
per cup of flour
1. hand mix until it resembles coarse oatmeal
2. add water, a little at a time, using a meat serving fork, like you have in your flatware set, until all is moistened
3. cut 2 pieces of waxed paper, long enough for below and above
4. put 1/2 or more of the pie dough between the sheets of waxed paper and roll out to fit your pie plate
5. pull the top sheet of waxed paper and put aside
6. put the pie plate upside down on top of the crust, and revert
7. use a paring knife to cut the excess crust from the sides, and add to the rest of the dough
8. fill with the filling
9. dot with butter on the top.
The butter mixes with the sugar, juices and flour and "candies" your pie
10. roll out the remainder of the dough between the sheets of waxed paper, peel off the top layer of waxed paper and put the crust on top of the filling.
11. Cut the excess and pinch two crusts together.
12. Use your paring knife to cut vent holes, dust with sugar, if you wish. Sometimes you can take the leftover pie crust and cut pie decorations with cookie cutters, like autumn leaves or, Christmas things, or...dare I say it...I have a PIG cookie cutter!

Bake at 350 degrees for 25-35 minutes, let cool and ENJOY!!!
I only use cornstarch to make cherry pie filling.