There is no pattern, it's just a basic top down raglan. My mom was the one who shared her "recipe" and I made a few sweaters like that. But I found that sleeves were too wide and for this one I used Yarn Harlot's proportion for sleeves/body.
I cast on a number of stitches between two front raglan lines (sleeve 1, back, sleeve 2) and knit flat adding one stitch at the beginning and the end of every other row to make a V-neck. When I had the same number of added stitches for the front than those for the back, I joined the ends and knit in a round from that point on. (Note to self, and possibly some others: adding one stitch every three rows will make a deeper V and you won't have to worry if the head will go through)