acorn, a corn

Acorn or acorn ( one word ) means the little nut that falls from oak trees--
An acorn hit him on the head as he was walking under the oak tree.
A squirrel is burying an acorn in the garden.

Acorn may also mean a kind of squash--
She made acorn squash soup; it's better than it sounds.

A corn or a corn ( two words ) describes something made of maize ( corn )--
They are building a corn maize for the party.
Our dog ran into a corn field, and we can't find him.

A corn may also mean a sore, usually on the foot; a type of callus--
He went to the podiatrist because he has a corn on his foot.

Now that you know that, you can say--
"They served each guest a corn casserole topped with an acorn."