Question:
Do one take Challa on a mixture of dough 2lb flour and 2lb oats
Answer:
Hello,
Yes, you would take off challah but without a bracha. Although they are two types of flour, since it is one dough they do combine together. The issue here is the fact that the dough is 4lb., which is enough to take off with a bracha according to R' Chaim Naeh, but not enough for a bracha according to Chazon Ish. That being the case, unless your minhag is to do like the smaller shiur, (R' Chaim Naeh), you would not make a bracha until you have almost 5lb.
Best wishes
Sources:
Yore Deah 324-1, 2