3. In a larger bowl, use an electric mixer to cream together butter, sugars, and vanilla on medium speed until light and fluffy, scraping down frequently. Take care not to overbeat.
4. Add flour mixture to creamed butter and sugar and mix on low speed until combined. Mix in oats, followed by drained raisins and egg.
5. Use a ¼-cup measure to scoop dough onto a parchment-paper lined baking sheet. Flatten each blob with base of measuring cup.
6. To bake cookies: Bake until cookies are golden-brown on the outside but still soft in the middle, about 17 minutes. Remove from oven and let rest on baking sheet a few minutes, then transfer to a rack to cool.