This phrase let’s us say things like, “Out of all my school subjects, I like history the most”. This piece of grammar or sentence structure is practically guaranteed to come up on the JLPT N5 examination.
【Group】の中では、【A】が一番【Adjective】
But first let’s just look at a few examples of 一番 on its own. It means “number one” but used with an adjective it turns it into a superlative.
| 一番早い。 | 
| The fastest/earliest. | 
| 一番かしこい。 | 
| The cleverest. | 
| 一番高い。 | 
| The most expensive. | 
Using the structure above we can come up with the following sentences.
| 同級生の中では、由美子が一番かしこいです。 | 
| Out of my classmates, Yumiko is the cleverest. | 
| 私は教科の中では、数学が一番好きです。 | 
| Of all my school subjects I like mathematics the best. | 
| 記憶の中では、一番寒い冬です。 | 
| The coldest winter in memory. | 
Note that 中 is a kanji you will see often. It means “middle” and the reading on its own is なか.