1. Preheat the oven to 325 degrees. Set the pie crust on the counter to warm up while you prepare the filling.
2. In the bowl of a stand mixer, beat the butter, sugar and brown sugar on medium speed until combined. Add in the eggs and mix until combined.
3. Add in the flour and salt, scraping down the sides if needed. Mix in the chocolate chips and walnuts.
4. Spread the cookie dough mixture into the pie crust, spreading the top to make it even.
5. Bake for 50-55 minutes.
6. Let cool for at least 2 hours.
7. Place hot fudge in a microwave safe dish and microwave for 10-20 seconds, until it is just runny enough to drizzle.
8. Transfer to a piping bag (or ziploc bag with the edge cut off) and drizzle hot fudge over the cake.
9. Slice and serve, topped with vanilla ice cream.