1. Preheat oven to 300F.
2. Cream together softened butter and sugar for 1 minute in a stand mixer until just smooth.  Scrape down the sides. Mix again.
3. Add vanilla. Mix another few seconds to incorporate.
4. Add all-purpose flour, rice flour and salt.  Add any flavorings at this time (see notes).  Mix on medium speed just until the dough comes together, and starts to pull away from the bowl.  Scrape the dough out and pat it into a flattened square.
5. On a floured surface, silpat, or floured piece of parchment, roll as evenly as you can to 1/2″ thickness. (Alternatively you can form it into a long “brick”, refrigerate, then slice- see notes)
6. Trim the edges and cut into 1 x 3-inch pieces. Poke holes if you like using a fork or toothpick. ( Or feel free to use a cookie cutter, reusing the scraps.)
7. Carefully space out 2 inches apart on a parchment-lined sheet pan using a metal spatula for this.  Chill the entire tray of cookies for 30 minutes in the refrigerator, or place in the freezer for 15 minutes.
8. Place the cold tray of cookies in the oven.  Bake for 30 minutes.  Let rest on the tray for a few minutes and move to a cooling rack.  They will crisp up as they cool.

To Store

Make sure cookies are completely cool and store in a covered container for up to two weeks at room temperature. Freeze up to 3 months.