E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To rule the roast. To have the chief direction; to be paramount.
It is usually thought that roast in this phrase means roost, and that the reference is to a cock who decides which hen is to roost nearest to him; but the subjoined quotation favours the idea of council.
John, Duke of Burgoyne, ruled the rost, and governed both King Charles and his whole realme.Hall: Union (1548).