On this day in 1773, infuriated colonists calling themselves "The Sons of Liberty" boarded ships and threw 342 chests of tea into the Boston Harbor. Known as the party that sparked a revolution, the tea party was an act of resistance against the Tea Act that the British Parliament had passed earlier, and a monopoly called the East India Tea Company that was underselling local merchants.
Preheat the oven to 350 degrees and place a rack in the center. Spray a 9-inch square metal pan with flour-added baking spray or line the inside with nonstick foil.
Mix the flour, salt, baking powder, cardamom, ginger, cinnamon, cloves, and nutmeg together in a small bowl; set aside. In the bowl of a stand mixer fitted with a paddle attachment, or in a large mixing bowl, using a handheld electric mixer, beat the butter and sugar on medium speed until creamy. Beat in the vanilla and sour cream. Reduce the mixer speed and beat in the egg and banana until creamy. Scrape the sides of the bowl. With the mixer on low, gradually add the flour mixture. When the flour is absorbed, mix in the chocolate chips and walnuts.
Spread in the prepared pan and bake for 28-30 minutes, or until the bars are browned around the edges and appear set. Let cool completely in the pan. Cut into 16 squares.