In a large mixing bowl, pour the cold heavy whipping cream and sweetened condensed milk. Beat with an electric hand mixer on medium-high speed until the mixture forms soft, frothy peaks — about 3 minutes. Add the fresh lemon juice and lemon zest, and gently fold it into the whipped mixture to combine. Fill a large glass halfway with ice cubes, then spoon the whipped lemonade mixture over the ice. Add a splash of cold water if you'd like a thinner drink, or leave it thick and creamy like a dessert. Garnish with extra whipped cream, lemon slices, and a sprig of mint for a refreshing, café-style treat. Serve immediately and enjoy the ultimate summer indulgence!