Alfajores are a favorite South American treat made of dulce de leche (caramelized milk) sandwiched between buttery shortbread cookies. An adaptation from Carnation. NOTE: Can substitute ready made dulce de leche for a quicker version.
Preheat oven to 350 degrees and grease 2 large baking sheets.
Pour 1 can (14 oz.) sweetened condensed milk into top of double-boiler pan. Add cinnamon stick. Place over boiling water. Cook over low heat, stirring occasionally, for 2 hours, or until thick and caramel colored. (Some additional water will be needed for bottom pan of double boiler). Remove from heat; remove cinnamon stick.
Sift cornstarch, flour and baking powder together into medium bowl; set aside.
Beat butter and sugar in a medium mixing bowl on medium speed until creamy. Add yolks; mixing well. Add lemon zest and brandy. With wooden spoon, mix cornstarch mixture into butter mixture to make a soft dough. If it is too soft (should not be runny), add some additional flour. With floured hands, form dough into a ball. Cover with plastic wrap; refrigerate for 30 minutes.
Roll dough on lightly floured surface to 1/8-inch thickness. Cut dough into at least 34, 2-inch circles. Reroll dough as necessary. Place circles on prepared baking sheets.
Bake for 10 minutes or until set; careful not to brown. Remove to wire racks to cool completely.
Spread about 2 teaspoons Caramelized Milk to flat side of half the cookies. Top with remaining cookies to form sandwiches. If desired, allow some of the Caramelized Milk filling to squeeze from the sides or spread more around the sides to roll in coconut, nuts or cocoa powder.
Cookies will keep in the refrigerator for several days or up to 3 months in the freezer.