The invention includes methods of forming at least a portion of a golf ball core, and the golf balls prepared thereby, by mixing a resilient polymer component, a free-radical initiator system, and a crosslinking agent to provide a first mixture, forming the first mixture into a plurality of shells (2) having a desired shape, first heat curing the shells (2) at a temperature to impart a rigidity sufficient to maintain the desired shape until the shells (2) are assembled and subsequently heat cured, quenching the first heat curing by reducing the shell temperature to inhibit crosslinking while a sufficient amount of free radical initiator system is present to facilitate a second heat curing, providing a center (5), assembling at least two shells (2) concentrically about the center (5) to form a first mantle layer (22), wherein the first mantle layer (22) and center (5) together form the ball core, and second curing the core at a temperature and for a time sufficient to further crosslink the first mixture and to at least crosslink the shells (22), thereby forming a cured golf ball core.