I teach it as three, but as with other words such as “chocolate” and “average”, I point out that if they occasionally hear an extra syllable, that is not considered wrong. As for “comfortable”, I believe three syllables is best (and is used on the US East Coast as well as in RP), but point out that a lot of Americans pronounce it as four syllables. Also note that the G in "vegetables" usually de-voices to match the T in the next syllable.
Here's one for you: How about the word "sandwich"?