The superlative of fashionable is "most fashionable."
most fashionable
I am fashionable.
yes very fashionable.
That is a very fashionable hat!
They're not fashionable now.
Fashionable Nonsense was created in 1997.
Fashionable Lectures was created in 1872.
Comparative: more fashionable Superlative: most fashionable
When referring to clothes: à la mode [parmi] = fashionable [among, with] When referring to restaurants, or resorts: chic [parmi] = fashionable [among, with]
From researching what the question has asked, there are no information about whether toast can be fashionable or not. As toast is food, it is highly unlikely that it would become fashionable.
the most fashionable company is totally north face