Octave-spanning, 12.5 fs, (1.9 cycle) pulses with 115 mu J energy in the short-wavelength mid-infrared spectral range (1-2.5 mu m) have been generated via phase-mismatched cascaded nonlinear frequency conversion using organic DAST (4-N, N-dimethylamino-4 '-N '-methylstilbazolium tosylate) crystal. Such ultrafast cascading effect is ensured by the interaction of a pump pulse with the exceptionally large effective nonlinearity of the DAST crystal and experiencing nonresonant, strongly phase-mismatched, Kerr-like negative nonlinearity.