I think you can start making hardened brick as soon as you have the resources.
10 stone = 1 brick.
Mix Ichor and Twine in the Firebowl Cauldron to make brick hardener.
I’m not sure of the ratio, but you’ll get a ton of hardening agents out of it.
I think it’s 10 agents for each ichor and twine cooked, but I’m not sure on the ratio of twine and ichor.
(1+1 I think).
Then add brick hardener to the furnace when you’re making bricks.
In making hardened bricks, it’s 1 brick + 1 hardener (at least with an smelter thrall but having one isn’t a prerequesite).
When the furnace is finished baking bricks, it will start baking hardened bricks.
For Gruel:
Mix Plant Fiber and Seeds in a camp fire, large camp fire or bond fire.
Doesn’t take a lot to make a lot of gruel.