太……了 is a specific structure that doesn't necessarily translate to "Too..." For example, 太好了 would translate as Great! Fantastic! Awesome! 我太爱你了 would translate as I love you soooo much. This structure puts emphasis on what's between 太 and 了. This sentence here would better translate as "It's super bitteeeeer" while your face is distorting itself you are desperately looking for something better to put in your mouth to get rid of the taste. It's much more expressive than "It's too bitter" that sounds like you're just making a statement and trying to adjust your (or somebody else's) cooking

My thought exactly

苦极了 is also correct (with the meaning of extremely) but I've been told it's not used very often in everyday speech