With mixer combine butter and sugar until combined, add in egg and vanilla. Mix in salt, flour, pumpkin, pumpkin pie spice and cinnamon until batter is smooth. Spread in greased pan.
Bake for 25-30 mins until center is cooked. Let cool.
For the frosting, melt the butter in a saucepan over medium heat. Add the brown sugar and milk and stir until it comes to boil (you can turn the heat to medium high if it's taking too long to boil). Remove from heat and let cool for 5 mins. Whisk in powdered sugar. Spread on top of blondies and allow frosting to set for 5 mins, then cut.
Recipe by THE SEMISWEET SISTERS at http://www.thesemisweetsisters.com/2016/08/26/pumpkin-blondies-with-brown-sugar-frosting/