One of my fave jams.
It all started many years ago when where I had a cabin up in the mountains the roses were out at the same time as the cherries.
You know the best way to see if some ingredients fit to be in the same jam? The way I do it is to put all of them with the sugar as well on a plate, smash them in my hands and try the whole thing. This will give you a pretty good idea about how the jam will be like when it will be ready.
Also you will get a good feeling about how much sugar to use. If it all feels too sweet then add less sugar. In general you do not really need to follow a recipe when you make a jam...
Later though when I was looking into it I realised that Ferber the famous French jam maker has a similar recipe in her book. In her recipe though she chooses the yellow harder cherries.
It is a bit hard to make as you have to remove the pits of the cherries but I believe it is worth it!!