We report on a passively mode-locked oscillator based on an erbium-doped dual concentric core fiber combining high normal dispersion and large mode area. This large normal dispersion laser generates long pulses with 30 ps duration and 0.17 nm spectral width at 1530 nm wavelength. The source delivers an average power of 64 mW at a repetition rate of 16 MHz, corresponding to 4 nJ energy. This concept opens up new degrees of freedom in the design of mode-locked fiber lasers.