YSK: “Milktoast” and “milquetoast” mean the same thing, and both are accepted spellings.
Why YSK: Before correcting someone for writing “milktoast” or "milk-toast" know that Collins Dictionary explicitly lists them as a variant spelling of “milquetoast”, meaning a meek, submissive, or timid person.
The unusual spelling comes from Caspar Milquetoast, a timid comic-strip character created in 1924 by H. T. Webster. His name was a play on milk toast, the bland dish of toast served in warm milk.
The character was created over a hundred years ago, and I suspect most people writing “milktoast” are thinking of the blandness of the dish rather than the comic strip. Personally, I’d be happy to see the more straightforward spelling catch on, especially since dictionaries already recognize it. #education