The buffer layer has been used, for the first time, in the cold-seeding melt-growth (MG)process for REBCO superconductor bulks. In this modified method, a mini pelletwas inserted between the seed and the bulk precursor. Notably, the chemicalcontamination, from the seed material (either REBCO films or SmBCO/NdBCOcrystals), was mostly absorbed by the mini pellet. Thus a uniformly highTc REBCO bulk was readily gained. Secondly, the higher limits of the maximum processing temperature(Tmax) were evidently raised, which is promisingly beneficial for broadening the growth window andovercoming the self-nucleation in the growth of large-sized bulk. In short, the success of thiswork is that it protects the bulk from seed-induced contamination, and breaks the limit ofTmax caused by the intrinsic properties of the seed material. By means of this simple seed/bufferlayer/precursor construction, we successfully fabricated a large single grain of GdBCO bulksuperconductor with a diameter of 56 mm.