Preheat oven to 350ºF, and line an 8-inch square baking dish with parchment paper.
Whisk together the flour, cornstarch, baking soda, baking powder, spices, and salt in a medium bowl; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and both sugars for 2 to 3 minutes, until pale and fluffy. Beat in the egg, followed by the molasses, maple syrup, and vanilla. Slowly add the dry ingredients, mixing until just combined.
Bake in the oven for 14-16 minutes, or until center looks dry and edges are slightly browned. Allow to cool completely.
Make the Frosting:
In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter together on high until smooth and creamy. Add the Irish Cream and vanilla and continue beating until combined. Add the powdered sugar, a half cup at a time, beating until fluffy.
Spread frosting onto completely cooled blondies. Cut into squares. Serve and enjoy!
Notes
*Feel free to add more Irish Cream if it's not strong enough to your liking! The flavor of the Irish Cream does get stronger as it sits in the frosting, so try not to go overboard.