What does 且 mean by itself?
将奶黄放入一个大，浅且可置于冷冻库的容器 means 'put the custard into a huge, shallow container (and) which can be put into a freezer'. 

So here 且 means and(而且).

Another useage 且 means 'just', such as 且行且珍惜(just cherish what you have at the moment) here 且 means just.

即可(离火) means you can do something when something happen as soon as possbile.

Such as: 
1. 当油热了，即可离火 (When the oil is hot, you can turn off fire right now[She suggest you do it right now]).
2. 开袋即食 (Open the bag, you can eat it)

即 has a meaning of you can do something with a hint do it now(as soon as possible).