I made this blanket for my little one year old son when I found out I was pregnant.
EDIT: A few corrections because it turns out I still have baby brain!
I didn't follow a pattern, so I'm just going by memory. (turns out my memory wasn't great, hence the edits)
I used 4ply yarn and my trusty 4mm hook. This is a bigger hook than what is usually used for this size yarn, resulting in a looser stitch.
foundation chain approx 150 stitches (I didn't count, just continued until it was the desired length)
I then alternated rows with
double crochet and treble (US)
treble and double treble (UK)
The important thing to remember is to get the correct turning stitch
At the start of the double (US) /treble row(UK) 4 chains
At the start of the single(US)/double (UK) row 3 chains
for a slightly smaller but similar effect you could try alternate rows of
single crochet and double (US)
double crochet and treble (UK)
and the turning chains are 1 for single (US) /double (UK)
and 3 for double (UK) and treble (UK)
(clicking on the links will take you to my tutorials)
and did this until I had a size I was happy with!