Hello - i as unable to find the link or the name of the free pattern, but here are the pattern rows, Pattern row 2 is where it states about stitching in the base of ch1.
Shawl - With 6.00mm hook ch150, change to 5.50mm hook, (RS) work 1sc in 2nd ch
from hook, * skip 1ch, 1 shell (see abbrev) in next ch, skip 1ch, 1sc in next ch, * rpt from * to * to end. Turn. (37 shell groups).
Pattern Row 1 - 3ch, * 1 vst (see abbrev) in ch space of shell, 1dc in sc, * rpt from * to * to end. Turn. (37 vst).
Pattern Row 2 - ch1, 1sc in base of ch1, * 1 shell in vst, 1sc in dc, * rpt from * to * to
last vst and 3ch, 1 shell in vst, 1sc in top of 3ch. Turn.