Traditional style cornice and modern combined cornice and light pelmet should be positioned so that they cover the doors in their run of wall cabinets.
Where a length of cornice/pelmet butts up to a returning wall, simply cut to length and pre-drill the rear section of the moulding before screw fixing it into the wall cabinet.
If you need to mitre an internal or external corner into your moulding, we strongly suggest that you do this with a powered precision saw. Do not attempt to cut a mitre joint by hand.
When you have cut the mitred lengths lay them out on the kitchen floor and glue the faces of each joint before taping together. Leave the tape on until the glued joint is set, then pilot drill and screw fix the finished assembly to your wall cabinet.