i took out the inside with 4 bites in an arrangement like:
OO
OO
except that they all connected to completelytake out the cetner, and then carefully take off the edges, u gotts get as much of the outside as possible in each bit, you have to precise or it wont be enough, i had a few crumbs but they allow you some

I got 15. Took me a few tries, also. I actually used the 4 bites in the middle as well.