1. Open a new image

Filter>Noise>Add Noise
Settings:
Amount= up to 400%
Distribution=Gaussian
Monochromatic=checked

2.  Filter>Pixelate>Mosaic

The size for this is 12. You can make cell size any size, although larger sizes can be downsized later.

3.  Now go to Filter>Stylize>Glowing Edges

Settings:
Edge Width = 2
Brightness=10
Smoothness=9 (how round the corners become)

4. Add Color:

Image>Adjust>Hue/Saturation
Make sure the Colorize box is checked