"We've been cooking a lot. We have dinner nights and we hang out," the Boardwalk Empire star, 35, tells PEOPLE.
"Just by birthright, I love pastas, so I cook a lot of that – lasagnas and meatballs. But she's into this whole Tex-Mex thing, which I've been catching on to. Guacamole and sour cream, quesadillas and tacos – we're experimenting."
A winner at the awards, with his hit HBO show taking home the Actor for ensemble in a drama series, Piazza was thrilled to have his girlfriend of seven months by his side.
"It's a great feeling. You want to share special things with special people," he explains. "I'm more than happy [with Ashlee]. She's a wonderful girl."
"I'm just happy to be here with my man," Simpson, 27, demurred before chatting about her expectant sister, due this spring.
"She's amazing. She's doing great," the actress and singer – who recently launched a tween fashion line with Jessica – tells PEOPLE. "She's having fun being pregnant and enjoying it."
Reporting by BLAINE ZUCKERMAN