Answer:
a) baked into a cake
Step-by-step explanation:
Baked into a cake showcases the purpose (the reason) of the batter, or the meaning of the batter. The rest of the answers don't define anything. Finally ready isn't the meaning, in the kitchen isn't the meaning and my party is not the meaning.
Also, with background knowledge, we can infer that the meaning of batter in this sentence most likely coincides with the meaning we know, which is a semi-liquid consistency baked into a solid. (cake, cupcake, brownie, etc)