A method of manufacturing an aircraft aerofoil such as a winglet. The aircraft aerofoil includes: a first cover, a second cover, an aerofoil leading edge, and an aerofoil trailing edge where the first and second cover are joined at a trailing edge interface. The first cover is formed by: a lay-up step in which a plurality of fibre plies are laid up to obtain a preform, wherein the preform has a thickness and a preform trailing edge, and the preform is laid up during the lay-up step with a ramp of decreasing thickness where the thickness of the preform decreases towards the preform trailing edge; and a curing step in which the preform is cured to form the first cover, wherein the ramp of decreasing thickness cures during the curing step to form a contact surface of the first cover.