We describe an innovative design of the spectral-phase-interferometry-for-direct-electric-field-reconstruction (SPIDER) technique applicable to the simultaneous measurement of the electric field of two ultrashort pulses, e.g., a reference and probe pulse. We demonstrate the utility of the device by measuring material dispersion in a single shot by subtracting the reconstructed phase of a dispersed pulse and a reference pulse and by quantifying phase differences arising from nonlinear effects. Our two-beam technique is particularly suitable for use in experiments performed on high-energy, ultrafast laser systems operating in a single-shot mode with significant pulse-to-pulse variations.