We present a detailed analysis of jet substructure observables such as the energy correlation function and the jet angularity for heavy-flavour jets in quantum chromodynamics (QCD). In specific, we study these observables to demonstrate the so-called dead-cone effect, i.e. the suppression of collinear QCD radiation around a massive quark within an angle proportional to the mass. We present our analysis at next-to-leading-logarithmic accuracy matched to fixed-order contributions to obtain an improved description of the transition around the dead-cone threshold. We also compare our analytical results with \texttt{PYTHIA}, \texttt{HERWIG} and \texttt{SHERPA} Monte Carlo predictions.