Various techniques to release the superficial MCL (sMCL) during medial open-wedge high tibial osteotomy (MOWHTO) has been introduced. However, there have been debates regarding the extent of sMCL release in MOWHTO. The authors present a pie-crust technique that involves selective and gradual release of sMCL from inside using a small, round-tip blade after opening the gap. The aims were to introduce our novel technique regarding sMCL release and evaluate the clinical and radiologic outcomes. One-hundred sixty-six knees underwent this procedure. With a mean 60.3 months’ follow-up, clinical scores were significantly improved after index operation (p<0.001). Hip-knee-ankle angle, medial joint opening, joint line convergence angle, and weight-bearing line ratio significantly improved after MOWHTO (p<0.05) and there were no significant changes during the follow-up period. No cases of valgus progression were observed. This technique would be a safe and effective method for selective and adequate release of sMCL in MOWHTO.