Not hollow, but definitely airier and meltier in the center. I'm not sure how big the small ones are (never seen them), but you can see the "original" proportions here (https://s-media-cache-ak0.pinimg.com/originals/5a/ec/a0/5aeca0254e24e0ccfabb06c0159e4fc1.jpg) (and the kind of airy/moussy filling here (https://alifelikeours.files.wordpress.com/2015/01/a9e1_timtambiscuitbite__minisite.jpg?w=640))

...and now I want a Tim Tam /o\ I'm from Israel, and over time Tim Tams became so popular in Israel by word-of-mouth of Israeli tourists in Australia, that the company started to produce a line of kosher Tim Tams so they cold be imported here in bulk.

/is maybe obsessed