High density internal transport barriers with peaked density profiles have been produced at JET by optimizing the pellet fuelling, heating power, current drive and plasma start-up. The scenario was developed with moderate momentum input and comparable ion and electron temperatures. Both features aim at matching the conditions envisaged for a burning plasma regime. Current and density profiles, which both appear to influence transport barrier formation, were independently controlled. The optimization recipe included early lower hybrid current drive followed by an Ohmic or neutral beam heated pellet fuelling gap. The internal transport barrier was then formed at the start of a high power additionally heated phase. Typical plasmas were at a toroidal field of 3 T and plasma current of 2 MA, corresponding to a peripheral safety factor q95 ≈ 5. Particle and energy transport were analysed by a 1.5 dimensional code including a pellet ablation module and a criterion for the barrier formation. Results of turbulence simulations with global electrostatic and electromagnetic fluid codes and a description of the observed magnetohydrodynamic instabilities are also reported.