Preheat your oven to 350 degrees F. Grease a 9-inch x 13-inch baking pan (glass or metal) and set aside.
Prepare the brownie batter according to package directions. Pour the brownie batter into the prepared baking pan.
Bake for 20 minutes (or 10 minutes less than the package directions indicate).
While the brownies bake, mix together the sugar, corn syrup, eggs, butter, and vanilla in a medium mixing bowl. Stir in pecans.
After brownies have partially baked, remove the pan from the oven and pour the pecan pie filling over the top. Spread the topping into an even layer.
Place the brownies back in the oven and bake for 25 to 35 minutes or until the filling only jiggles slightly in the middle when you move the pan.
Remove the brownies from the oven and let cool to room temperature before cutting into 20 squares.
Notes
If you can't find a family-size brownie mix (for a 9x13 pan), you can substitute 2 regular brownie mix boxes (for an 8x8 pan) plus their listed ingredients.