Cornelian cherry (Cornus mas L.) fruits are a valuable source of bioactive compounds that are responsible for the perception of bitter taste of chocolate products. The aim of the study was to validate the inhibitory effect of Cornus mas on the TAS2R3 and TAS2R13 bitter taste receptors and to assess the effect of masking the bitter taste of dark chocolate with the help of the sensory panel. Dark chocolate was prepared with an addition of 5% of freeze-dried cornelian cherry fruits and 108 CFU/g of Bacillus coagulans probiotic strains. Effect on the TAS2R receptors was evaluated in specially transfected HEK293T cells, and the inhibition ratio was measured using the calcium release test. Moreover, the total polyphenol content, antioxidant activity and simulated intestinal in vitro digestion were determined for the samples. The tested chocolate products were rich in chlorogenic, caffeic and sinapic acids. The addition of cornelian cherry positively affected the antioxidant activity. The phytochemicals of Cornus mas decreased the TAS2R13 activity by 132% after a 2-minute interaction and, % at the same time, inhibited the TAS2R3 activity by 11.5. Meanwhile, chocolate with the addition of fruit was less bitter according to the sensory panel.