A subview will always be drawn on “top” of its superview.
Depending on your specific requirements, you may need to have a plain UIView as the background/container view, with your existing subviews in there, and then your custom view as another subview added to the very top, so it has the highest Z-order.
This would work, for example, if your custom view was a grid overlay that should be on top of everything else. The custom view would have to be non-opaque with a clear background colour.