What is the correct way to punctuate the sentence? Ivan handed me a stale bun ___ which was too hard to eat ___ so I joked that we use it as a hockey puck instead.

Ivan handed me a stale bun, which was too hard to eat. So I joked that we use it as a hockey puck instead.

Explanation:

The sentence above was punctuated with a comma and a period.

The comma was used to separate the sentence adverb from the rest of the sentence. This is because whenever a word or a sentence indicates a "way" of something, a comma is used and the characteristic of the old bread, presented a "way", a way of modifying the noun "bread", so a comma should be used. Soon after, a period was used to indicate that one thought was concluded and another thought would be started.