Astronauts on the International Space Station have baked the first cookies in space, but they took far longer than on Earth.

The space station's Italian commander Luca Parmitano acted as the baker aided by NASA astronaut Christina Koch for the chocolate-chip cookie experiment.

Usually, cookies take around 15-20 minutes to bake on Earth, but the astronauts discovered that their most successful efforts required at least two hours in the oven while in space. The first batch of cookies was in the oven for 25 minutes and the second for 75 minutes, but they were still under-baked.

The best results came from 120 and 130 minutes in the oven.

"We made space cookies and milk for Santa this year," Koch tweeted.

The prototype oven, which can be used in microgravity, was designed and built by Nanoracks and Zero-G Kitchen, while the DoubleTree by the Hilton hotel chain supplied the raw cookie dough.

"The ISS smelled like fresh chocolate chip cookies when @astro_luca opened the oven door! Just like home!" Nanoracks tweeted.

"While we have initial visual and scent feedback from the crew aboard the ISS, we're excited to dive into fully understanding the baking results – including breaking down why the bake time and temperature in space varies from what we are used to seeing on Earth," Mary Murphy, a Nanoracks payloads manager, said in a statement from the Hilton.

While the astronauts said they looked and smelled like cookies, no one has tasted them.

Three of the cookies returned to Earth on the SpaceX Dragon spacecraft on Jan. 7 and will undergo testing by food scientists to determine if they are edible.

"Currently on the International Space Station there's really a limited ability to prepare foods in the ways that we're used to," Zero-G Kitchen founder Ian Fichtenbaum said in a video posted by Hilton.

"And now as longer duration space flight is more common you want to focus on making space more comfortable," added co-founder Jordana Fichtenbaum.