  We present numerical simulations of high-order harmonic generation in helium
using a temporally synthesised and spatially non-homogeneous strong laser
field. The combination of temporal and spatial laser field synthesis results in
a dramatic cut-off extension far beyond the usual semiclassical limit. Our
predictions are based on the convergence of three complementary approaches:
resolution of the three dimensional Time Dependent Schr\"odinger Equation,
time-frequency analysis of the resulting dipole moment and classical
trajectories extraction. Employing a combination of temporally and spatially
synthesised laser field provides coherent XUV photons beyond the carbon K-edge
which is of high interest for initiating inner-shell dynamics and study
time-resolved intra-molecular attosecond spectroscopy.
