Boston Cream Pie

1 1/2 cups milk

1/3 cup granulated sugar

2 tablespoons cornstarch

1/8 teaspoon salt

2 teaspoons vanilla

Baking spray with flour to grease pan

1 1/4 cups all-purpose flour or 1 1/2 cups cake flour

1 cup granulated sugar

1/3 cup butter or margarine, room temperature

3/4 cup milk

1 1/2 teaspoons baking powder

1 teaspoon vanilla

1/2 teaspoon salt

1 large egg

3 tablespoons butter or margarine

3 oz unsweetened baking chocolate

3 to 4 tablespoons water

1 cup powdered sugar

3/4 teaspoon vanilla