I used 4ply yarn and an E hook (3.5mm) and began with 91 (fairly loose) chain. This gave me a 17” wide blanket, which ended up 18” square when I’d added a shell border. I worked the blanket in one shade, but you could stripe it in different pastel shades to use up oddments if you prefer.
Instructions:
Work 91 chain, [or any multiple of 6 + 1]
Foundation row:
Work 3 trebles into the 4th chain from the hook. Miss 2 chain then work 1 double into the next chain, 2 chain, * miss 2 chain, 3 treble into next chain, miss 2 chain, double into next chain, 2 chain; repeat from * to the end of the row, ending with a double into the last chain. Chain 3 turn.
Pattern row:
3 trebles into the first double. Miss 2 trebles then 1 double into the next treble, 2 chain; repeat from * to the end of the row, ending with 1 double into the last treble. Chain 3 turn.
Repeat this pattern row until the piece of work is the desired length – I wanted my blanket to be square, so worked for 17”. Fasten off, and work a border if required. I find a simple shell border, or just a couple of rounds of doubles, neatens up the edges well, and makes the piece look “finished”