In a heavy saucepan, beat eggs, 1/2 cup sugar, and flour. Gradually beat hot milk into egg mixture. Cook, stirring constantly, over medium heat until sauce thickens, about 5 minutes.
Remove from heat. Add butter and vanilla and stir until well blended. Place plastic wrap directly over filling to keep top from hardening; let cool.
Fold freshly cut bananas into the cooled filling, reserving a few slices for garnish, if desired. Toss reserved slices with lemon juice to coat, to prevent turning brown. Spoon mixture into the baked and cooled pie shell. Whip cream and blend in the confectioners' sugar. Spread over the top of the pie. Arrange banana slices over the top with a few mint leaves, if desired.
Keep leftover pie refrigerated.
Calories per serving: 478