Single-crystalline thin films of a new highly optically nonlinear organic material, N-(4-nitrophenyl)-(L)-prolinol (NPP), have been grown between transparent silica plates. Their calibrated thickness is 11 µm, but they can be made thinner or thicker with single-crystalline areas of the order of 10 mm2. Transverse second-harmonic generation measurements have evidenced the high efficiency of the material and allowed for the measurement of both the d21 and d22 coefficients. The value d21 = 200 x 10-9 esu is, to our knowledge, the highest phase-matchable coefficient ever reported for a material with transparency extending from 0.5 to 2 µm. The configuration explored here can be readily used, after minor modifications. for waveauided nonlinear interactions.