Rowan berries can taste quite sour and bitter so it's not easy to come up with recipes. In the old days Finnish people used to dry these berries and eat them during hard times so that they could get their vitamins. In fact, rowan berries contain three times more vitamin C than oranges.
It was my first time trying this, so I ended up doing just a little test. I picked the berries from my nearest forest (two minutes walk).
300g cleaned rowan berries
1dl water
2dl jam/jelly sugar
2tsp vanilla sugar
1. Clean the berries from dirt and branches.

2. Put the berries and water into a pot and start boiling until steam rises out of them. Add the jam and vanilla sugar.
3. You can crush some of the berries using e.g. fork. Boil the jam about 5 minutes and mix at times. Separate the foam forming on top of the jam if you want to.
4. Boil with medium heat 5 minutes more.
5. Take the pot away from the heat and let it cool down a bit.
6. Can the jam in a clean and hot jar.
7. Let the jam cool down. Preserve the jam in the fridge.