Combine the sugar, cornstarch and salt in a medium saucepan and whisk to combine. Stir in the milk. Set over medium-high heat and cook until thickened and bubbly, stirring constantly. Reduce the heat and continue to stir for 2 more minutes. Remove from the heat.

In a medium bowl, lightly whisk the eggs. Slowly whisk in about 1/2 cup of the hot mixture, whisking constantly. Return all of the mixture to the saucepan and return to the heat. Bring to a gentle boil, then cook and stir for 2 minutes longer.

Remove the pan from the heat and stir in the butter and the vanilla. Let the mixture cool slightly, then press plastic wrap directly on the surface of the custard. Refrigerate for 30 minutes, or until almost room temperature.

Slice the bananas. Spread half of the custard in the bottom of the baked pie crust. Top with a single layer of banana slices. Pour the remaining custard over the top of the bananas. Cover with plastic wrap and refrigerate for at least 6 hours.

Combine the raspberry preserves with 2 tablespoons of warm water. Stir in half of the fresh raspberries.

Remove the plastic wrap from the pie and spread the raspberry mixture over the top. Sprinkle the remaining fresh raspberries on top.

Pie can be served immediately or refrigerated until ready to serve.