Start by bringing all the ingredients to room temperature. To ensure this, leave them on the kitchen counter for half an hour. Next, grab a large enough bowl and start beating the erythritol (or sugar) and butter together. Beat until you get a fluffy consistency. While you are doing this, melt the chocolate. Melt it using a technique called a bain-marie. Otherwise, you risk burning the chocolate.
In order to melt the chocolate properly, you need to put a saucepan on the hob and add some water. Make sure it comes up to 5 cm to the side of the pan. Then, bring it to a boil, then lower the heat until the water simmers. Put a heatproof bowl on top of the saucepan and add the chocolate. It will melt gradually. But make sure you stir from time to time.
Next, add the melted chocolate to the sweetened butter and mix well. Then, add the flour, salt, vanilla extract, cocoa powder, and, finally, the quail eggs. After you obtain a smooth batter, fold in the sour cherries. If the mixture feels too stiff, add a couple of tablespoons of milk. If not, don't add anything more.
Next, pour the mixture into a buttered brownie tin and pop it in the preheated oven (160 degrees Celsius or 320 Fahrenheit). Bake for 25 to 30 minutes on low heat until the brownies are coming away from the side.
Allow them to cool a little and then take them out. Sprinkle with more dark chocolate or whatever you want and you're done.