  It has been proposed that Type Ia supernovae (SNe Ia) that are normal in
their spectra and brightness can be explained by a double detonation that
ignites first in a helium shell on the surface of the white dwarf (WD). This
proposition is supported by the satisfactory match between simulated explosions
of sub-Chandrasekhar-mass WDs with no surface He layer and observations of
normal SNe Ia. However, previous calculations of He-ignited double detonations
have required either artificial removal of the He shell ashes or extreme
enrichment of the surface He layer in order to obtain normal SNe Ia. Here we
demonstrate, for the first time in multi-dimensional full-star simulations,
that a thin, modestly enriched He layer will lead to a SN Ia that is normal in
its brightness and spectra. This strengthens the case for double detonations as
a major contributing channel to the population of normal SNe Ia.
