[Grammar] Why do we use 'that' and 'which' at the same time?

[Heidi L]

(an excerpt from Studio Classroom, Jan 2021)

The most important element of this environment, that which gives Shirakawa-go its distinct character, is snow. Indeed, one of the best times to visit is when the snow has transformed the area into a winter wonderland.

Is it correct that both that and which are used here?

 

[Tdol]

It's fine. If you moved snow to earlier in the sentence, you would only need which:

The most important element of this environment is snow, which gives Shirakawa-go its distinct character.

However, I would use distinctive.