What do you do with the cookie jar?

You just produce items as usual and then you might get a single cookie which is gonna produce energy. Firstly you need 3 then 10 and so on. But I don't know yet what you can do with pile of them as I've maxed that and can't do anything with this yet

You collect cookies merge until pile is correct amount. Put into cookie hat get gems and energy. Some sell off the cookies fir energy but you get.more energy and gems by collecting and filling cookie jar.

Jar level one i.think is a stack of two. Add in 2 cookie piles until full to claim rewards.

Then it's 4 cookies per pile. Put several piles in jar to collect full rewards. Jar does show required cookie level. ;-)

Repeat it's not always double the previous and it starts off lower again

I found it! Ya know the area where you accumulate tool boxes? The cookie jars are in there!