  The detonation of an overlying helium layer on a
$0.8-1.1\,\mathrm{M}_{\odot}$ carbon-oxygen (CO) white dwarf (WD) can detonate
the CO WD and create a thermonuclear supernova (SN). Many authors have recently
shown that when the mass of the He layer is low ($\lesssim
0.03\,\mathrm{M}_{\odot}$), the ashes from its detonation minimally impact the
spectra and light-curve from the CO detonation, allowing the explosion to
appear remarkably similar to Type Ia SNe. These new insights motivate our
investigation of dynamical He shell burning, and our search for a binary
scenario that stably accumulates thermally unstable He shells in the
$0.01-0.08\,\mathrm{M}_{\odot}$ range, thick enough to detonate, but also often
thin enough for minimal impact on the observables. We first show that our
improved non-adiabatic evolution of convective He shell burning in this shell
mass range leads to conditions ripe for a He detonation. We also find that a
stable mass-transfer scenario with a high entropy He WD donor of mass
$0.15-0.25\,\mathrm{M}_\odot$ yields the He shell masses needed to achieve the
double detonations. This scenario also predicts that the surviving He donor
leaves with a space velocity consistent with the unusual runaway object, D6-2.
We find that hot He WD donors originate in common envelope events when a
$1.3-2.0\,\mathrm{M}_\odot$ star fills its Roche lobe at the base of the red
giant branch at orbital periods of $1-10$ days with the CO WD.
