Kohlrabi and Flank Steak Stir-Fry

My mother used to serve kohlrabi in stir-fries when I was growing up. The first time I saw the plant growing, she had taken me to visit some older woman who, I think, may have belonged to the Quaker meetinghouse where I had to spend many Sunday mornings sitting silently in a circle. The woman’s home was somewhere near Cranbrook, a local private school whose environs had the only hills in town. She had a large garden on the side of one of those hills with all sorts of vegetables growing in i