Sift the flour, baking soda, and salt together in a bowl. In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with an electric mixer, mix the butter on medium speed for about 2 minutes. Add half of the sugar and zest mixture and turn the mixer up to medium high. Mix for 2 minutes, then add the remaining sugar and mix for 4 minutes, making sure to scrape down the bottom and sides of the bowl with a rubber spatula periodically. The butter and sugar should be very light, fluffy, and fragrant.