'Oh! I'll have a raw egg!' 'Just one?' 'Yes. If I run out I'll just ladle myself more.'
Literal
''Ah. I raw-egg!'' ''One is-okay [question-ですか]?'' ''Yes. Not-enough-become-[when-たら] again pour-add-[because-から]''
A restaurant/diner exchange. 生卵 is 'raw egg' — eaten in Japan as a topping for rice, noodles, or sukiyaki, where raw egg safety standards are high enough for raw consumption. 注ぎ足す (つぎたす) is a compound verb 'to pour and add, top up'. 足りなくなる ('become insufficient') uses the verb 足りる ('to be sufficient') + ~くなる (become adjective). The speaker omits the verb 'order/have' — あたし生卵 = 'I'll (have) raw egg'.