Put blueberries with sugar, lemon juice in a pot and simmer at low temperature for 5 minutes. Finally, finely puree with an immersion blender and let stand.
Whip the cream until stiff and leave it in the fridge.
Finely chop the chocolate, melt it over a double boiler, and set aside.
Melt the butter and let it stand to cool down a bit.
Finely crush the cookies and mix with the butter.