In a food processor or blender, puree blueberries then transfer to a medium saucepan. Working over medium heat, add sugar, lemon juice, and lemon zest. Bring mixture to a boil then reduce heat. Simmer until slightly reduced, about 15 minutes.
Transfer to a bowl and place in refrigerator to chill, 1 to 2 hours.
In a large bowl using a hand mixer, or in the bowl of a stand mixer fitted with the whisk attachment, beat heavy cream until stiff peaks form. Fold in sweetened condensed milk until fully combined, then fold in chilled blueberry puree.
Transfer to 9"-x-5" loaf pan and freeze until firm, 5 hours.