In a medium saucepan, combine all the ingredients for the blackberry sauce. Bring the mixture to a boil over medium heat. Reduce the heat and simmer for 15 minutes, stirring occasionally. Remove from heat and cool completely. Set aside.
In a small saucepan, combine cream and lavender flowers. Bring the mixture to a gentle simmer. Remove from heat and strain mixture. Cover and place in the refrigerator for 2 hours.
Place the lavender cream in a large bowl. Add the cheese and sugar. Beat at low speed until all ingredients are incorporated. Increase the speed and beat until the mixtures reaches medium peaks.
Spoon a layer of lavender mousse into four individual serving cups. Pour one layer of blackberry sauce on top. Continue layering with cream and blackberry sauce. Garnish with fresh blackberries, lavender flowers, and mint.