Chuck your nutella in the fridge or the freezer long enough for it to be cold and heavy but not too long that its completely frozen.

Put in the flour, cocoa powder and sugar into a mug and mix them up.

Break an egg into the mug, add in the milk and mix. It doesn't have to be perfectly mixed.

Add 3 teaspoons of olive oil to the mix.

You can add a tablespoon of nutella and swirl it around so there will be chocolate swirls. You can also throw in chunks of frozen baking chocolate. Or use Hershey's chocolate/caramel sauce. This step is optional.

Put in a tablespoon (or a chunk) of frozen Nutella at the top of the mix. It should slowly sink.

Chuck the mug in the microwave oven for a couple of minutes, maybe 3 depending on how gooey or spongey you want your cake to be.

The cake should rise up to the top of the mug. You can add another slab of Nutella on the top if you want. Enjoy!