If you’ve knit top-down shawls before, you’ll probably know the classic way of starting one: with a garter tab cast on.
But if you want the shawl to have an i-cord edge, you need an i-cord tab:
Provisionally cast on 3 sts
Knit a short i-cord with your working yarn as follows:
R1: k3, slip stitches back on left needle
Rep. last row four times more
R6: k3, pick up 3 sts along the left side of the i-cord (from the left leg of the third i-cord stitch), then unravel the provisional cast on an slip 3 stitches onto your needle wyif and in reverse order (with the WS facing forward). – 9 sts
Repeat R1 only 3 times more, then only pick up and knit 1 stitch from i-cord and 3 sts from provisional CO: 7 sts in total