Adulteration of extra virgin olive oil (EVOO) with refined olive oil (ROO) is a widespread fraudulent practice that compromises product quality and consumer trust. Conventional methods for detecting such adulteration are often time-consuming and require extensive sample preparation. This study proposes a rapid, reproducible, and sensitive approach using Differential Scanning Calorimetry (DSC) to detect the presence of ROO in EVOO. Thermograms were recorded for pure EVOO, pure ROO, and binary mixtures at different proportions (5–50% ROO in EVOO). Characteristic melting and crystallization transitions were analyzed to identify thermal markers indicative of adulteration. The results demonstrate that DSC can detect as low as 10% ROO in EVOO through distinct shifts in onset and peak temperatures as well as enthalpy changes. The method requires minimal sample preparation, offers rapid analysis (<30 min), and provides a reliable fingerprint to distinguish adulterated EVOO.