D7 Views 3 Blog Archive Block
You'd have to create 2 views, one which takes Year argument with path base_path/yyyy and another that takes 2 arguments with path base_path/yyyy/mm

And you have to create a custom module which defines a hook_block_info and hook_block_view. This block will basically read your node table for blog type posts, and build links to the 2 views you created above, structured in Year > Month hierarchy. I'm not sure if there's an easier way to achieve this.