4. Then grate the frozen butter, one third at a time, directly into the bowl with the dry ingredients. Toss to coat the butter and repeat the grating and tossing until you have grated all the needed butter
11. Place the cookie sheet with the flans into the preheated oven and bake for 20 minutes (do not open the oven door). Check at exactly 20 minutes: if the center looks glossy and wet, add 5 more minutes to the baking time. When the extra time has elapsed, immediately take out the baking sheet and leaving the cookies in the flan pan(s) place the pan(s) onto a wire cooling rack to cool completely to room temperature in the flan pan(s)
12. When the cookies have cooled to room temperature, gently press on the removable bottom, and then use an offset spatula (or very thin knife) to gently lift the cookies off the bottom of the pan. Place the cookies onto the wire cooling rack to air dry for about 18 to 24 hours for best results. Enjoy!