  In this work using three-dimensional particle-in-cell simulations and
analytical considerations we demonstrate intense high-order plasma surface
harmonics carrying a time-varying orbital angular momentum (OAM) -- the
self-torque. We show that by using two laser beams with different OAMs $l_1$
and $l_2$ and a certain delay between each other and shooting them obliquely on
an overdense plasma target, one can generate harmonics with OAM spanning $nl_1$
to $nl_2$, where $n$ is the order of the harmonic. Such intense self-torqued
harmonics can offer new possibilities in ultrafast spectroscopy.
