
As part of our kitchen reno, we extended a portion to the edge of the wall.
This left a gap between the ceiling and new cabinets so I had to build an extension to the bulkhead.
Steps
Step 1

I removed parts of the cornices at the edges where I planed to extend them only (no photo) using a chisel and hammer.
Step 2

I built a three sided frame including a base that attached to the upper side of the cabinet below. This aligned with the existing wall and bulkhead.
Step 3

I then cut some pieces of cornice to size using a mitre box and hand saw and glued them on using construction adhesive.
I also applied some plaster to tidy all the joints up.
Step 4

Then I taped the wall and ceiling sections and painted them separately.
Step 5

Completed the paint work and the bulkhead and cornice look like they've always been there.