Disclosed is a molding unit for the forming of a container provided with a hollow recess toward the interior of the container, including: a mold provided with a lateral wall defining a cavity having the impression of at least one portion of the container, provided with a housing formed hollow in a protrusion forming a projection toward the interior of the cavity and opening into the cavity; and a boxing device having an insert mounted in translation relative to the lateral wall between a retracted position in which the insert is retracted in the housing, and a deployed position in which the insert projects outside of the housing, a projection whose transverse extension is less than or equal to 85% of the cumulative transverse extension of the protrusion and of the insert.