Prepare a cake pan with a 21 cm of diameter. I recommend using baking paper. Use the same mug for the whole recipe. Preheat the oven to 170℃.
In a bigger bowl, mix flour, sugar and oil until it's crumbly - take out probably the ¾ of a mug out of the crumble.
Add an egg, baking powder and milk to the rest of the mixture in the bowl. Give it a good stir until it has a consistency of a regular cake mixture. It should be thick but also runny.
Pour the cake mixture into a cake pan. Open a jar with poppyseed stuffing and mix it with cherries. Add it to the cake mixture by using a tablespoon. Try to add a tablespoon of poppyseed stuffing with cherries to every part of the cake.
On top of the cake add the crumble from the mug. I also added a few extra cherries on top of the cake.
Bake for 50-55 minutes or until the toothpick comes out clean. Take the cake out of the oven and let it cool completely.