Soaking the raisins in warm water rehydrates them slightly, leaving you with a softer cookie that can be a nice change of pace from the typical chewy texture.
How to Make It
Preheat oven to 350°.
Place raisins in a small bowl, and cover with warm water. Let stand 5 minutes. Drain.
Weigh or lightly spoon flours and potato starch into dry measuring cups; level with a knife. Combine flours, potato starch, and next 7 ingredients (through salt) in a medium bowl; stir with a whisk.
Place sugars and butter in a large bowl; beat with a mixer at high speed until well blended. Add vanilla and egg; beat until blended. Gradually add flour mixture, beating at low speed until blended. Add raisins and oats; beat until blended.
Drop dough by tablespoonfuls 2 inches apart onto baking sheets lined with parchment paper. Bake at 350° for 12 to 14 minutes or until edges of cookies are lightly browned. Cool 2 minutes on pans. Remove cookies from pans; cool on wire racks.
Gluten-Free Baking; The Food Lover's Gluten-Free Cookbook