Heat the wild blueberries and sugar in a saucepan over medium heat.
Use a potato masher to break down the berries. Cook for 8-10 minutes or until the blueberry sauce has a thick jam-like consistency.
Remove the blueberry puree from the heat and cool to room temperature. To cool faster, transfer to a large bowl and refrigerate.
Beat the cream cheese and softened butter on medium speed until fluffy in the bowl of a stand mixer.
Starting on low speed, beat in the powdered sugar (work your way up to medium-high speed) until you have a thick and creamy frosting.
Mix in the vanilla extract into the cream cheese mixture.
Slowly beat in the blueberry reduction.
Transfer to a piping bag and decorate the top of the cupcakes, bundt cake, or layered cake.