Place strawberry marshmallows, vanilla yoghurt, and whole milk in a pot. Heat the mixture over the slow flame until the marshmallows are melted and all the ingredients are well-combined. Remove and cool.
Divide half of the fresh blueberries into two serving glasses, and slowly pour in the mousse. Cover and chill for an hour until set. Arrange the rest of the blueberries on the top of the mousse. Serve.