Preheat oven to 350 f. Then take your baking tin and spray with a non-stick spray (or grease it with butter). You can then line the pan with parchment paper. The parchment paper makes it easier to lift out of the pan later but it is not necessary, this is an optional step.
Put the butter and the peanut butter into a microwavable safe bowl and microwave until you have melted butter. Set aside until ready to use.
In a mixing bowl, add the eggs and whisk the eggs with the brown sugar and the white granulated sugar until it is nice and thick. Add the vanilla extract and whisk a bit more. Add the melted butter and the peanut butter to the mixture and continue to mix together. Then, add the dry ingredients (baking powder, flour), and chocolate chunks. Use a spatula to fold the mixture together. The blondie batter will come together and be the color of peanut butter.
Transfer the blondie batter to your baking pan. Sprinkle the salt on top, and place in the oven. When baking in an 8x8 pan, bake for 35 minutes. If you are using a 9x13 baking pan then bake for 45-40 mins. If it does not seem done, place back in the oven for 5-10 more mins.
To check for doneness, remove the baking pan from the oven, insert a toothpick into the middle. If the toothpick comes out clean, then it means it is baked. Allow it to cool completely in the baking pan and then lift it out once it has cooled completely. If the blondies feel too soft, it likely means that they are underbaked. You want a gooey center but they should not be so soft that they are falling apart. You can always cut a little piece from the blondies, taste it, and see if it truly is done. If not, you could place it bake in the oven for 10 minutes and check again.