Preheat your Traeger Grill to 325F.
Start by adding room temperature butter and light brown sugar to the bowl of a stand mixer. Cream the sugar and butter together using the paddle attachment until the ingredients have combined completely.
Next, add the eggs one at a time. Turn the mixer on low to combine. After the first egg has mixed in completely, add the second egg.
Use a spatula to scrape down the sides of the bowl.
Add the heavy cream and vanilla. Turn the mixer on low to combine again.
Now it's time for the dry ingredients. Add ¾ cup of flour, the salt, and baking powder. Turn the mixer on low to combine all of the ingredients.
Remove the bowl from the stand mixer.
In a separate bowl, combine the toasted walnuts, butterscotch chips, and the other ¼ cup of flour. Stir them together so that the walnuts and butterscotch chips are evenly coated with the flour. This step prevents the butterscotch chips from falling to the bottom of the blondie batter while they bake.
Using a spatula, gently fold in the butterscotch chips and chopped walnuts to the blondie batter.
Pour the blondie batter into a 9" cast iron skillet.
Once the Traeger has reached 325F, place the cast iron skillet on the grates in the center and close the lid. Cook the blondie on the Traeger with the lid closed for 1 hour. Check for doneness by poking a toothpick into the blondie. If the toothpick comes out clean, the blondies are done.
Remove the blondies from the Traeger and allow to cool for 15 minutes.
Serve the blondie family style out of the skillet with vanilla ice cream and caramel sauce.