  We present freestanding metasurfaces operating at optical frequencies with a
total thickness of only 40$\,$nm. The metasurfaces are fabricated by focused
ion beam milling of nanovoids in a carbon film followed by thermal evaporation
of gold and plasma ashing of the carbon film. As a first example, we
demonstrate a metasurface lens based on resonant V-shaped nanovoids with a
focal length of 1$\,$mm. The second example is a metasurface phase-plate
consisting of appropriately oriented rectangular nanovoids that transforms a
Gaussian input beam into a Laguerre-Gaussian ${LG_{-1,0}}$ mode.
