1. In a saucepan, cook the blueberries in butter for 5 minutes.
2. Add the sugar and let it cook for 10 minutes over low heat.
3. Let it cool and reduce it to a puree using a mixer. Pass the mixture through a sieve to keep only the liquid, squeeze the pulp to extract as much as possible.
4. With an electric whisk, extend the white cheese with milk and whip the mixture for 4 minutes. Fill the verrines with this mousse and refrigerate for 30 minutes.
5. Once out of the fridge, place the blueberry jelly on the mousse and serve.