Banana Cream Pie

• 3/4 cup white sugar
• 1/3 cup all-purpose flour
• 1/4 teaspoon salt
• 2 cups milk
• 3 egg yolks, beaten
• 2 tablespoons butter
• 1 1/4 teaspoons vanilla extract
• 1 (9 inch) pie crust, baked
• 4 bananas, sliced