In a medium saucepan, heat milk over medium heat until bubbles form around edges of hte pan. Set aside and cover to keep hot.
In a blender or food processor, puree the bananas, lemon juice and 1/4 cup sugar until smooth. Set aside.
In the blender or food processor, beat the remaining 1/4 cup sugar and egg yolks until thick. WIth the machine running, gradually add the hot milk. Return the mixture to the sauce pan.
Cook over medium-low heat, stirring constantly with a wooden spoon 6 to 8 minutes or until the mixture thickens and coats the back of a spoon. Remove from heat and place pan in the bowl of an ice bath. Stir for 2 minutes to cool. Then stir in banana mixture. Cover and chill for at least 2 hours or until thoroughly chilled.
Transfer the mixture to an ice cream maker and freeze according to manufacturer's instructions.