In a medium saucepan over medium high heat, bring the blueberries, sugar, and lemon juice to a boil. Reduce heat and gently boil for 5-10 minutes. Use the back of a spoon to gently smash the berries against the side of the pan.
Remove the blueberry mixture from the heat and cool completely.
Using an electric mixer, beat the heavy whipping cream until stiff peaks form.
To a large bowl, stir together the sweetened condensed milk and vanilla extract. Gently fold in the whipped cream. Add the cooled blueberry mixture and stir just until combined.
Pour the mixture into a loaf pan and cover the top with a piece of wax or parchment paper. Freeze for at least six hours or overnight before serving.
To use frozen blueberries, thaw first and drain before cooking.Keeps well for two weeks.