“Leftover biscuits” might be a rare word pairing, but just in case you’ve (Artisan), the award-winning co-owner of Back in the Day Bakery shares clever tricks (like her grandmother’s genius method for baking last night’s mashed potatoes into tomorrow’s dinner rolls), practical advice about butter temperature and rolling pin weight, and a complete roster of treats, from buttermilk waffles to savory oyster potpies to three entire chapters on cakes to, for the holidays, sweet boiled custard doused in bourbon.