Dad's Banana Cream Pie

2/3 cup sugar
1/4 cup cornstarch
2 tablespoons flour
1/4 teaspoon salt
1 egg
1 tablespoon butter
1 teaspoon vanilla
3 cups milk

Mix first four ingredients. Add 1/2 cup milk and mix until smooth. Add rest of milk and cook until boiling. Boil 2 minutes. Add beaten egg while stirring briskly. Cook one minute longer. Add butter and vanilla. Cool to room temperature. Pour into baked crust layered with bananas (about 2 for a large pie.) Serve with whipped cream. Garnish with banana slices.