Thickness of skim plaster

I have a hole in an internal wall that I need to block up with some bricks.
if I cement the bricks in place, can I put skim directly on the bricks?
How deep is ok for the thickness of the skim?
I know that usually it is a couple of mm, but I will probably have to set the bricks back by about 1cm from the surface. Is that too thick for plastering?
Or should I set them back further allowing for a small piece of plasterboard to be stuck on first?
Thanks

1cm is fine if you put a bonding coat on first, then when that's dry a final skim coat to bring it to level. Alternatively, go with the ~15mm inset and plasterboard, quicker solution as no need for drying out time between coats.

1cm is too thick for a skim coat not to sag before setting.

Thanks for that.. any suggestion on how to fix the plasterboard to the block?
Its a small area, maybe 30cm x 30cm.
So nailing or screwing may not be so easy.

Use construction adhesive, the type you get it in tubes for use with sealant guns.