This DIY is quick and easy and comes at the request of a fan who is just 12 years old ;-) her names is Jessie and she kindly asked that I do this for her. It is super easy and shown in step by step pics below.
TOOLS: Old or new loose fitting t-shirt, ruler, scissors, ribbon, pins, 1 safety pin, scarp piece of fabric in a similar weight and content.
Mark the half way point on the back of the t-shirt and measure.
Cut a piece of scrap fabric using the measurement you took for the back x 2" wide.
Roll up the front of the shirt so it stays out of your way
Pin your scrap to the inside of the shirt (back) and align in the center.
Thread your machine with a matching color thread.
Sew 3/8" from the long edge on each side
Sew a straight line down the center
You should have 3 lines
Cut a 36" piece of ribbon and pin the safety pin to the end of the ribbon
Insert from the bottom up one side
Then go back in on the other side from the top and out of the bottom.
Pull both ends to create the gathering. You can pull as much or as little as you want.
Fold over 3/8"" and pin until you create 3 pleats in the center of the sleeve
Once pinned take it to the sewing machine
Sew down the middle of the pleats and backstitch to secure. REMOVE your pins as you get to them. NEVER sew over pins.