Sift flour into a medium bowl, then add sugar, instant dry yeast, salt, and baking soda; whisk until well combined . Add the butter, toss to break up the pieces, and, using your hands, smash each cube flat. Continue smashing and rubbing until the butter has mostly disappeared into a floury mix, although a few larger, Cheerio-sized pieces may remain. This can also be done with 4 or 5 pulses in a food processor, just take care not to overdo it. The prepared mix can be refrigerated up to 3 weeks in an airtight container, then used as directed below.
