Melt butter over low heat. Add sugar and stir till completely dissolved. Remove from heat and stir in vanilla and 1 cup of the chocolate chips. Add flour and banana to butter/sugar mixture and mix to thoroughly combine. Stir in remaining chips and 1/4 cup of the walnuts. Pour into graham pie crust. Heat the raspberry preserves for 1-2 minutes. Drizzle over top of pie and sprinkle on the remaining walnuts. Bake at 375 degrees for 45 minutes.
**Note: If pie looks a little liquid-y when you take it out, don't worry. Once it cools, it will set. You can speed up this process by popping it in the fridge.**