This week when I harvested some kale for dinner, instead of just taking a few leaves, I chopped the entire top off the plant including a length of stem with it.
I took each piece and pressed it down into the soil, leaving about 2 inches of stem above ground. With the leafless stem pieces, I needed to be sure to plant them the right direction instead of upside down. Luckily the leaf scar is crescent shaped making it easy to tell up from down.
Spacing....my beds are 40 inches wide. Thus I opted to plant four cuttings across the bed about 10 inches apart. Each row of 4 was spaced about 12 inches apart.
Now we wait and see what happens.