My father is good at cooking. As for my mother, she's good at eating.

Literal

Father [topic-は] cooking [subject-が] skilled. Mother [speaking of-はといえば], eating [subject-が] skilled.

~はといえば ('speaking of, as for') introduces a contrasting topic — here pivoting from father to mother with humorous effect. 得意 (skilled/good at) takes が for its object.