Step 1: Brown the Butter. Melt unsalted butter in a medium saucepan over medium heat, stirring continuously for 5-7 minutes until golden brown.

Step 2: Mix Wet Ingredients. Combine cooled brown butter with sugars, then mix in the egg, yolk, and vanilla until smooth.

Step 3: Combine Dry Ingredients. Whisk flour, salt, and baking soda in a separate bowl, then gently fold into wet ingredients until no dry flour remains.

Step 4: Add Oats and Raisins. Fold in oats and raisins gently to avoid overmixing.

Step 5: Chill Dough. Refrigerate the dough covered for at least 30 minutes to thicken.

Step 6: Bake. Preheat oven to 350°F, line baking sheets, and bake for about 11 minutes or until edges are golden.

Step 7: Cool. Let cookies rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.