Can you cut a cake fairly to solve this middle school math problem?

[Pat Mustard]

When Poca, Alex, Rob and Whatshisname came for a visit, Losty baked a cake.  It was a square cake which she frosted on the sides and on top with yummy cream cheese frosting.  "I want a big piece of cake" said Poca.  "Just make sure my piece has a maximally quantum-big portion of frosting" said Alex.  "Be fair!" exclaimed Rob.  "Whatever" said Whatshisname.

How can Losty cut the cake so as to give all five of them the largest piece possible with each containing an equal share of both cake and frosting?  Oh, and to keep it interesting, lets do it with the fewest possible straight cuts with a knife (so no, you can't dump it all in a blender and measure out equal shares of sludge).  Surprisingly (hint, hint) the dimensions of the cake are irrelevant but if you really, really want to know, the size of the actual cake is given below.

---

The cake was 20 cm on each of its four sides and 5 cm tall.  Good luck .. and be fair!

---

*Edited to clear up the fact that the entire cake is to be used up making these five equal servings.  Thank you: 

Anomalocaris 

The definitive answer:

---

While Losty was busy greeting her guests Tazzycorn snuck in the back window and ate all the cake. Therefore all five of them got nothing, the maximal amount each of what was left of the cake.

---