2) The flour base. 

3) The milk carton.
4) A metal mold because it can be reused and has a long use time.

THE STEPS:
1) First, we have to make a sponge cake:
1. Separate the whites from the egg yolks and reserve in separate containers.

2. Add the butter with the sugar in a bowl and mix.
3. Then, add the previously reserved yolks to the butter and sugar mixture and beat.
4. In a other bowl, mix the flour with the baking powder.
5. Add the half of the mixture of flour and baking powder and half of the milk and beat again.
6. After everything has been incorporated, we add the rest of the milk and flour and the vanilla essence to the mixture. Mix until you get a soft dough.
7. Beat the whites until you get meringue and add them to the final mixture.
8. Finally the mixture is added to a container, we give it a few strokes and we take it to the oven at 180 degrees for 40 minutes.
9. When the cake is ready, decorate. And enjoy!

2) When you have the cake ready, start recycling some of the packaging.
1. First wash the metal mold with as little water as possible and let it dry, the mold material is much more environmentally friendly.
2. Then, wash the milk carton very well. When it is dry, put a little soil on it and use it as a pot.
3. The flour wrap should be shaken really well and then reused as a container for other things like nuts.
4. We are going to reuse the eggshells as compost for the plant soil that we planted in the milk carton. First let them dry in the sun, then crush them and finally spread them over the plant's soil.

And boom! you will have a delicious project to help the planet.