I can see Tony, upon realizing what fondue means, deciding it must be an old timey sexytiems phrase and trying to use it on Steve, who is legitimately convinced from then on that Starks like cheese and bread. He doesn't pick up on the sexual undertones because it's Steve and hey, Howard wanted the same food and he didn't date Peggy so it must be a craving!

Cue Steve fighting with the internet for a fondue recipe and, after failing, going out and acquiring a cookbook to teach him how to make this magical Stark attracting substance.

The real kicker is, Tony doesn't even like cheese. He just eats it because he doesn't want Steve to stop being nice to him.