  We advocate a search for an extended scalar sector at the LHC via $hh$
production, where $h$ is the 125 GeV Higgs boson. A resonance feature in the
$hh$ invariant mass is a smoking gun of an $s$-channel heavy Higgs resonance,
$H$. With one $h$ decaying to two photons and the other decaying to $b$-quarks,
the resonant signal may be discoverable above the $hh$ continuum background for
$M_H<$ 1 TeV. The product of the scalar and top Yukawa couplings can be
measured to better than $10-20\%$ accuracy, and its sign can be inferred from
the $hh$ lineshape via interference effects.
