Base rnd, each side: Any multiple.
Begin 1 st to left of corner st.
Rnd 1: Ch 3 (counts as dc), dc in each st around, placing 5 dc in each corner st, join with slip st to top of ch-3.
Rnd 2: Ch 4, FLtr in each dc around, placing 3 FLtr in each corner st — corner group made, join with slip st to top of ch-4.
Rnd 3: Ch 1, *Folding sc in each st to corner group, (insert hook into back loop of next tr and into back loop of Rnd-1 corner st and pull up a loop) three times, yarn over and pull through all 4 loops on hook to sc3tog; rep from * around, join with slip st to first sc.
Rnd 4: Rep Rnd 1. Fasten off.
The “folding” technique shown here is easy to master and makes a nice three-dimensional ridge. Incorporate the technique into your everyday crochet anywhere you would normally have a row of double crochet.