Have everything at hand.
Make a trapezoid shape cube (2.5 cm. base, 3 cm. upper side, 4 cm. length and 1.5 cm high).
Squash one side flattening it uniformly.
It should look like this...
Sink the cylindrical cutter (which should adjust to your finger) and remove it.
You can use a top, anything rigid should be fine.
Make round the edges.
Bake for 30 minutes and that's it.