Green’s Dictionary of Slang

stuffed monkey n.

(UK, East London Jewish) ‘a very pleasant close almond biscuit’ (Ware).

[UK]J. Ware Passing Eng. of the Victorian Era.
[UK]Dly Herald 21 Apr. 5/5: Stuffed Monkey. If you like a spicy almond flavour, you will vote this unusual pastry a huge success.