How to Make It
Lightly spoon cornstarch and flour into dry measuring cups; level with a knife. Whisk together cornstarch, flour, salt, baking powder, cinnamon, and red pepper in a bowl.
Combine butter and sugar in the bowl of a stand mixer; beat at medium-high speed for 3 minutes or until light and fluffy. Reduce speed to medium. Add egg yolks, 1 at a time, beating well after each addition. Mix in orange juice and vanilla. Add flour mixture; beat at low speed until combined. Turn dough out onto a lightly floured surface; press into a (1-inch-thick) rectangle. Wrap tightly with plastic wrap; chill 1 hour.
Preheat oven to 350°. Line 2 baking sheets with parchment paper.
Divide dough in half. Roll half of dough to 1/4-inch thickness on a well-floured surface. Cut into 40 cookies with a 2-inch round, scalloped-edge cookie cutter, rerolling dough scraps as necessary. Arrange cookies 1/2 inch apart on prepared baking sheets. Bake 10 minutes or until cookies are set. (Edges will not brown.) Let cool completely on wire racks. Repeat with remaining dough.
Flip 20 cookies over. Top each with 1 1/2 teaspoons dulce de leche. Top with remaining cookies. Sift powdered sugar evenly over sandwiched cookies.