The short answer is to build up a technical portfolio. Designers do this. There's no reason software engineers can't too.
Spend some time creating some small projects of your own. It doesn't have to be a particularly useful product, because you're not out to start a company. It can be something fun, or related to features you've built for previous employers.
For example, if you had to build a mortgage calculator for a previous employer, go build one for yourself. Don't worry about the UI if you're not a designer. Just get it working.
Or, if you like games, build a blackjack game or 2048 clone. You can even build some widgets, like a slideshow or image processor.
Ideally, these projects should cover the range of your skills. It will take time to build these, but they can serve as a great way to put your best foot forward when prospective employers ask for code samples.