hans89,
I believe that the mistake you made, was using the wrong pot for cooking millet on your stove.
You did not give us all the details, so I'm assuming that you were cooking your millet from scratch, meaning it had not yet been cooked, and therefore you were trying to bring the water the millet was cooking in up to a boil which means you were using high heat.
The casserole, I imagine is not made of metal or glass but instead clay or some ceramic material that is not designed for high heat cooking.
Clay cookware (like the
Chinese sappo, the
Spanish cazuela pots) or
Mexican terracota cazuela pots are for medium to low direct fire cooking and can only be used with high heat when baking in the oven since that heat is radiant or indirect heat.
So, I recommend that you use metal pots like
stainless steel,
pressure cookers. or
cast iron or pots made of
enamel and cast iron for cooking food using all heat levels on direct flame on your stovetop.
Also, you can use
Ohsawa Pots inside pressure cookers if you wish to cook whole grains, beans, and such from scratch in a ceramic environment.
Does this make any sense to you?
Thank you, very much.
Happy cooking!
Bruce Paine