A method and device for manufacturing an ice cream dessert that includes a built-in ice cream confectionery decoration deposited in the form of a gathered frill folded over on itself, the folds of which run alternately in one direction then in the opposite direction by extrusion from a set of moving nozzles with flattened end-piece with slot-shaped nozzle outlet placed above a moving support. The apparatus includes a source of cold ice cream composition supplying at least one extruded ribbon of ice cream composition at a temperature of −6° C. or below, a support for the set of moving nozzles which is given an oscillating movement transversely with respect to the moving support, and a mechanical device for setting the oscillating support in motion. The method can be practiced by operation of the device.