Among Siena’s most traditional Christmas cookies, cavallucci are not elegant or photogenic, lacking the bright colors, icing, and sparkling sugar we expect from a Christmas cookie. Nor do they come in Christmas shapes; they’re round and rustic, lightly flattened on the ends, floury and a bit lumpy. And yet, with that first bite full of warm spices, rich nuttiness, and sweet candied fruit, you’ll forget all about the presentation. These were my grandfather Remigio’s favorite cookies. Every time my mum went to San Gimignano during the holidays, she returned home with a paper bag with a couple of cavallucci that Nonno had sent us. Whenever I bake them now, I am brought back to those childhood Christmas holidays. The spiced smell lingers in the kitchen for hours, one of the most evocative aromas of Tuscan festivities. Makes 25 cookies   5 1/4 cups (650 grams) all-purpose flour 2 tablespoons (30 …