Preheat oven to 350°F. Place the butter and unsweetened chocolate in a microwave-safe bowl. Microwave in 30 second intervals until the butter is melted. Whisk to melt the chocolate.
Whisk in the sugar, milk, flour, corn syrup, vanilla, salt, and eggs until smooth. Fold in the nuts with a spatula.
Pour the mixture into the pie shell, and bake for 30–35 minutes. Let cool, then cut into slices and serve with ice cream, chocolate sauce, and sprinkles (if desired).
Notes
Don't have the time or ingredients to make the brownies from scratch? You can use store-bought brownie mix instead. Prepare it as directed on the box, pour into the pie shell, and bake it according to the package directions for an 8x8 inch pan.