Preheat oven to 350 °F
In a small saucepan, melt 2tbsp of butter. Add in 2 tbsp of brown sugar and stir to combine. Add in ½ cup of chopped pecans and stir to coat the pecans. Transfer to a small bowl and set aside.
In a small saucepan brown the 1/2 cup of butter. Do so by melting the butter over medium heat and continuing to stir the butter while it cooks further. The butter should start to make popping noises and start to smell nutty. Once the popping stops, remove from heat, and transfer to a large mixing bowl to prevent the butter from burning due to risidual heat in the pan.
Once butter cools, add brown sugar, vanilla, pumpkin, and an egg. Whisk until combined.
In a separate bowl, add flour, pumpkin pie spice, baking powder and salt. Stir to combine and add to the wet ingredients.
Stir until one uniform batter.
Add in the candied pecans and stir well.
Transfer to a greased 9x9 pan. Bake for 20-30 minutes or until a tooth pick comes out clean.
Remove from oven. Top with ½ bag of mini marshmallows.
Place back in the oven under the broiler setting and broil for 30 seconds to a minute. Make sure to keep an eye on it or the marshmallows can really expand and burn.
Let blondies sit for at least a half hour to let the marshmallows to set before cutting.