Dough, a part of which was baked

I prepared dough out of about 2.5 kg of flour. Most of it is for the home, but a small amount of it I am sending with my son to his Yeshivah. I put part of it in the oven and then I remembered that I forgot to separate the challah. What do I need to do now?

Dear …!
You can separate the challah even after baking. And if part of it is baked and part of it is not, it is better to separate from the part that is not baked for the entire amount, because the preferred way of doing this mitzvah is to separate from unbaked dough.
You should recite blessing [since the son is also part of your family, this is not considered 'a dough that stands to be divided'].