I am keen to try to replicate a new icecream out in Australia which is described as

"chocolate ice cream with chewy chocolate brownie pieces and swirled with a rich chocolate custard."

http://www.connoisseuricecream.com.au/tubs/

I can't eat it from the shops since it won't be gluten free.

How would you make a custard swirl?

I think I'm ok to make chocolate icecream (I have an icecream maker), the brownie components and the mechanism of adding everything together, but how to make a custard swirl - since many icecream recipes are custard based anyway and I want it a distinct component?

Current thoughts are to make a rich custard, possibly with a bit of added butter, and to add alcohol of some sort or just in vanilla extract form to try to keep the custard from freezing.

I know there are some amazing cooks on YLF - any ideas?