Step 1

Create a new document with white background. At what ever size you want. I use 600 by 600

Select another foreground color instead of black, I've chosen blue 146bb5. Then select the gradient tool and the radial gradient. Make a gradient from the middle of the document to the bottom. Your image should look like

Step 2

Go Filter > Pixelate > Crystallize and choose a cell size of 49 pixels. Now your image should look like this.

Step 3

Right click on the layer in the layers panel and duplicate it. On the new layer go Filter > Stylize > Find Edges and your image should look like this.