What you will need is: A donutty color you like, a small piece of pre cooked white clay, and some type of file. (the white thing is a shell, but don't use a shell. I couldn't find a piece of pre cooked white clsy big enough:P)
They will your donut colored clay, you form it into a donut shape.
<- see picture if you need help. I'm sure you don't:D
Now you grab your pre cooked white clay and your file.
file against the cooked clay (over a plate) and a little pile of white dust should begin to form:D
Now to make the powder on the donut you dab your finger in the white dust and pat it along each face and edge of the donut. You may need to file more clay. Cover the donut in the dust:)
Once covered in dust the donut should look like this.
put in oven for 15 mintues
And voila! theres your donut! and remember DON'T EAT IT! :D