01 -
Preheat the oven to 350°F. Line an 8 by 8-inch baking pan with foil or parchment paper, leaving an overhang.
02 -
In a medium microwave-safe bowl, microwave the butter until melted. Allow to cool until just warm (about 80°F). Once cool, whisk in the brown sugar, egg, vanilla, and pumpkin.
03 -
In a large bowl, combine the flour, cinnamon, ginger, nutmeg, baking soda, and salt.
04 -
Add the butter mixture to the flour mixture, stirring until just combined. Batter will be thick. Pour the batter into the prepared pan, spreading evenly with a spatula.
05 -
Bake for 25 minutes, or until a cake tester inserted into the center comes out clean. Be careful not to overbake. Set the pan on a wire rack to cool completely.
06 -
In a large bowl, use an electric mixer to beat the butter and brown sugar on medium-high speed until light, fluffy, and smooth. Use a spatula to scrape down the bottom and sides of the bowl. Add in the cinnamon and salt. On low speed, gradually add in the powdered sugar until incorporated. Add the vanilla and milk and increase the speed to medium-high. Beat until very light and fluffy, 2-3 minutes. Adjust frosting consistency with additional powdered sugar or milk, if needed.
07 -
Spread the frosting evenly over the cooled pumpkin bars. Cut into squares before serving. Store in an airtight container at room temperature for up to 1 day or in the fridge for up to 5 days.