Step 1: What you'll need + pattern cutting
First, you'll need to draw the pattern. I honestly just sketched one by hand. Cut it out and lie it on top of one of the pillowcases. Pin the pattern to the pillow case and cut.
Now cut the snow part off of the pattern, pin it to the white fabric and cut it out. (If you can tell, I cut two of them and that's only because I'm making two pillows.)