Donuts stuffed with ice cream was so 2014. A new dessert shop called Oh Oui! Pâtisserie has opened in Garden Grove and it stuffs macarons with a gelato of your choice. The shop doesn't seem to have a website and I've yet to make a trip, so I can't tell you how much one might cost. But since Oh Oui! is competing with the other Vietnamese bakeries in Little Saigon, I wouldn't bet that it'll cost more than what you'd pay for a typical macaron elsewhere in OC, even with the added gelato.
https://www.facebook.com/ohouipatisserie Macaron stuffed with ice cream!