Pulse figs and raisins in a food processor until finely chopped, then stir together with remaining filling ingredients in a bowl. Chill, covered, at least 8 hours. Whisk together flour, sugar, baking powder, and salt in a large bowl. Add butter and blend with your fingertips or a pastry blender (or pulse in a food processor) just until most of mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Add eggs, milk, vanilla, and zest and stir with a fork until a soft dough forms. Halve dough and gather each half into a ball, then flatten each half into a rough 6- by 4-inch rectangle between sheets of plastic wrap. Chill until firm, at least 8 hours. Preheat oven to 350°F. Roll out 1 rectangle of dough (keep remaining dough chilled) into a 15- by 14-inch rectangle on a well-floured surface with a floured rolling pin. Trim to a 13- by 10-inch rectangle (chill trimmings), then cut into 4 (10- by 3 1/4-inch) strips. Arrange 1/3 cup filling in a 1-inch-wide log lengthwise down center of each strip, then fold sides of each strip up over filling to enclose it, pinching edges together to seal. Turn rolls seam-sides down and press gently to flatten seams. Cut logs crosswise with a floured knife into 1 1/2-inch-wide slices and arrange 1/2 inch apart on buttered large baking sheets. Make more cookies in same manner with remaining chilled dough, trimmings (reroll once), and filling. Bake cookies in batches in middle of oven until golden around edges, 16 to 20 minutes. Transfer cookies to racks and cool until warm, about 10 minutes. Whisk together confectioners sugar, vanilla, and enough orange juice to make a pourable icing. Brush icing on warm cookies and decorate with nonpareils (if using), then cool completely. Available at some specialty bakeware shops and Sweet Celebrations (800-328-6722).