I used sugar and cream cotton for this blanket for ease of washing it, but any worsted weight yarn will work if it suites your purposes. You could also make two, smaller rectangles and make a poncho out of them. I used a 40″ size 8 circular needle for this project.
Start by casting on 3 stitches. For each row, Knit 2, YO, Knit to end of row.
When the sides equal the desired (I made mine 48″) width of the blanket (Point A), you are ready to turn your first corner:
Row 1: Knit 2, YO, K3Tog, Knit to end of row.
Row 2: Knit 2, YO, Kint to end of row.
This will make your blanket sides parallel until the longest side is the length you want the blanket (Mine was 72″) (Point B). At that point every row is K2, YO, K3Tog, K to end of row.
Continue in this way until you have three stitches left and bind off.
If you want to print this off so you can have the pattern with you, here is a pdf version of it. The Happy Blanket