To make the gingerbread bars: Preheat the oven to 350°F with a rack contained in the coronary coronary heart. Line an 8″ sq. pan with a parchment sling and frivolously grease.
In a medium bowl, whisk collectively the flour, gingerbread spice, baking powder, and salt.
In an infinite saucepan or microwave-safe bowl, warmth the butter over medium-low or microwave for 45 to 60 seconds, lined, on 50% energy, till merely melted.
Whisk the molasses and brown sugar into the butter. Add the egg and vanilla and whisk till the combination is shiny and emulsified.
Add the dry elements to the moist elements and whisk till easy. Change the batter to the ready pan and unfold it to realize the corners.
Bake the gingerbread bars for 20 to 25 minutes, till set contained in the coronary coronary heart.
Take away the bars from the oven and allow them to sit back barely contained in the pan earlier than utilizing the parchment to switch them to a wire rack. Let cool completely. (The bars could also be made 2 days prematurely; retailer hermetic at room temperature.)
To make the frosting: Working in an infinite bowl with a rubber spatula or handheld mixer or contained in the bowl of a stand mixer fitted with the flat beater, sift contained in the confectioners’ sugar and salt, then add the butter. Beat till a thick paste types. Add the water and beat till the frosting is simple and spreadable. Cowl till able to make the most of.
As shortly as a result of the bars are utterly cooled, unfold the frosting evenly excessive. (A small offset spatula is a useful software program program correct proper right here.) Working shortly earlier than the frosting fashions, adorn with sprinkles and/or gingerbread spice. Slice into bars and serve at room temperature.
Storage knowledge: Retailer leftover frosted gingerbread bars well-wrapped at room temperature for as so much as 3 days.