ELK GROVE VILLAGE, Ill.—Baking more than a billion doughnuts a year is no sweat for Krispy Kreme DNUT -0.85%decrease; down pointing triangle . The company manufactures its own equipment to shape, bake and glaze the shiny pastries it sells across more than 40 countries, and relies on relatively few workers. Cake crumbles, graham-cracker crust toppings and star-spangled sprinkles are a whole other challenge. Krispy Kreme has tried doughnut-decorating robots, and found they can’t beat the human touch.