1. Prepare the cookies: preheat the oven to 325° and move the racks as close to the centre as possible. Line two heavy, not non-stick, baking sheets with parchment paper and set aside. In a food processor, combine the flour, sugar, rice flour and salt and whir just to mix. Add the butter and vanilla and pulse until the mixture resembles a rough meal. Add the pecans and process until the mixture comes together in clumps when you squish it together. Depending on the size of the processor bowl, you may have to scrape the dough down the sides several times. Turn dough out onto a large sheet of parchment paper and press into a compact disc. The final dough will be dense and crumbly, but should hold together well when pressed firmly.
2. Roll the dough between two pieces of parchment paper to a ¼-inch thickness. Using a small 1- to 1½-inch cutter (I use a little star-shaped cutter for these cookies), cut the dough into shapes and carefully transfer them to the lined baking sheets with the help of a palette knife. Space the cookies about ¾ inch apart. Chill the filled sheets for 20 to 30 minutes, or until the dough is very firm. Bake the cookies for 12 to 15 minutes, or until the tops of the cookies are just firm and the bottoms are just barely beginning to colour. Cool for 5 minutes on the baking sheets, then transfer the cookies to wire racks and cool completely. (The cookies can be made up to this point up to 2 days ahead and stored at room temperature in airtight containers.)
3. Prepare the caramel filling: in a small, heavy-bottomed saucepan, combine all of the ingredients for the filling. Bring the mixture to a gentle boil over low heat, stirring constantly, until bubbles break the surface. Keeping the mixture at a gentle boil, and stirring constantly, cook the caramel for 2 minutes from this point, then remove the pot from the heat and allow the mixture to cool completely. (The caramel can be made up to 1 day ahead of time and stored in an airtight container in the refrigerator. Return it to the stove and bring it slowly back to just below the boil, stirring constantly, then allow to cool to room temperature before proceeding.)
4. To assemble the sandwiches, spread a scant teaspoon of the room temperature caramel on the underside of a cookie with a small palette or butter knife. It can be a sticky job, and I usually end up using a finger to secure the glob of caramel onto the cookie. Keep your fingers clean and dry, and the caramel shouldn’t stick too badly. Top the caramel with a second cookie, underside down, lining up any points or edges on the two cookies. Repeat until all of the cookies are sandwiched. Although they are best within a day or two, the filled sandwiches will keep in an airtight container at room temperature for up to 1 week.