Why are you guys packed into the corner like this?
My decision to quit Tofugu finally solidified.
I think the pudding will finally harden soon.
You've seen how 固める means "to make hard." This word means that something hardened by itself, it means to harden or to solidify.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading already so you should be able to read it!