Combine sugar and cornstarch in a pot; whisk in milk and lemon juice and heat over medium heat until mixture boils. Whisking continually boil 1 minute, until thick. Mix 1/2 cup hot mixture into egg and pour back into pot. Whisking continually, cook over low heat 1 minute.
Pour hot custard into pie crust and let cool. Chill pie 2 to 4 hours, lightly wrapped in plastic wrap. Top pie with kiwi slices just before serving.