If you're using fresh sour cherries, pit them first. Nowadays, there are special cherry pitters that make the job much easier. Whether you pit them by hand or with a tool, always check them carefully afterward to make sure no pits remain. Even jarred sour cherries can occasionally contain pits, so it's a good idea to inspect those as well.
First, prepare the spiced infusion. Pour 1 liter of water into a saucepan and bring it to a boil. Add the cinnamon sticks and whole cloves. Boil over high heat until the liquid has reduced by about half, creating a rich, concentrated flavor. Once it's ready, set it aside – you'll add it to the soup at the end.
In a large pot, bring the remaining 1 liter of water to a boil. Add the 150 g of sugar, the packet of vanilla sugar, and a pinch of salt to help enhance the flavors. Bring it to a boil, and while it's heating, prepare the flour mixture.
Thickening (roux mixture):Place the flour in a mixing bowl and add a small amount of the heavy cream. Mix it with a whisk. It’s easier to combine when there is less liquid at first. Once the mixture is smooth and lump-free, add the remaining cream and the sour cream. Whisk until completely smooth and free of lumps. Once the sweetened water has come to a boil, add the pitted sour cherries. (If you are using jarred sour cherries, you can also pour in their juice.) Let it simmer for a few minutes, but be careful not to overcook the cherries so they don’t fall apart.
Remove the pot from the heat and temper the thickening: take a ladle of the hot liquid and gradually add it to the cream mixture, stirring constantly. Then return the soup to the stove and pour the thickening through a sieve into the soup to ensure it stays completely smooth. Bring it briefly back to a gentle boil.
A few minutes after boiling, pour in the previously prepared spiced infusion through a sieve. Let it simmer briefly, then remove from the heat and allow it to cool. While cooling, you can adjust the flavor with sugar, vanilla sugar, or even a bit of red wine if desired.
Serving:Serve in pre-chilled bowls or cups, garnished with whipped cream.