How to Make It
Whisk together flours, hazelnut meal, and salt in a medium bowl; set aside. Using a heavy-duty stand mixer fitted with the paddle attachment (or a large bowl and electric hand mixer), beat butter, granulated sugar, and vanilla at medium speed until creamy, about 2 minutes. With mixer running on low speed, add flour mixture, beating until smooth. Divide dough in half, and pat each half into a disk. Wrap each disk in plastic wrap, and chill until cold, about 1 hour.
Preheat oven to 350°F. Line 2 large baking sheets with parchment paper. Unwrap dough disks, and discard plastic wrap. On a lightly floured work surface, carefully roll each dough disk to a scant 1/4-inch thickness. (Press dough back together if it cracks.) From one rolled-out disk, using a 2-inch square cutter, cut out 24 dough squares as close together as possible. Using a smaller square cutter, cut out centers of dough squares, reserving smaller center squares. Place larger dough squares 2 inches apart on one prepared baking sheet.
From second rolled-out disk, cut out 24 (2-inch) dough squares, rerolling scraps (including reserved cut-out dough centers) as necessary. Place 2 inches apart on second prepared baking sheet. Refrigerate all dough squares until chilled, about 30 minutes.
Bake cookies in preheated oven on middle and upper oven racks until very lightly browned and just firm, 15 to 17 minutes, rotating pans from top to bottom and front to back halfway through baking. Let cool completely on baking sheets, about 20 minutes.
Spread about 2 teaspoons marshmallow creme on each whole square cookie; cover each with a square cut-out cookie. Place chocolate in a microwavable bowl, and microwave at high until melted and smooth, about 2 minutes, stirring every 20 seconds. Transfer chocolate to a small ziplock plastic freezer bag. Snip 1 corner of bag to make a small hole; drizzle chocolate over cookies. Let cookies stand until chocolate is firm, about 2 minutes.