Salem

Can someone recommend the best solution to flattening this mine entrance (see pic) which is adjacent to clay tiles.

Hold shift and click on a corner to drop 1 layer of dirt on any particular corner.

I dont know if this has been fixed or not, but last I tried it worked:
Drop the dirt using ctrl on a corner that does not have clay and work your way towards the clay, you should be able to redig it make it flat.