2. Slice the bananas into ½-inch pieces and toss them with the brown sugar and butter in a 2-quart baking dish. Bake for 40 minutes, stirring once during baking, until the bananas are browned and cooked through.
3. Scrape the bananas and the thick syrup in the baking dish into a blender or food processor. Add the milk, granulated sugar, vanilla, lemon juice and salt, and purée until smooth.
4. Chill the mixture for at least 8 hour (or overnight) in the refrigerator, then freeze it in your ice cream maker according to the manufacturer's instructions. If the chilled mixture is too thick to pour into your machine, whisk it to thin it out.