Preheat oven to 350°F. Line baking sheet with parchment paper or Silpat.
Beat butter and sugars until fully combined and fluffy. Scrape down bowl with rubber spatula, then add egg and vanilla and beat until incorporated.
In a separate bowl, whisk together flour, baking powder, baking soda, salt, and oats. Add flour mixture to the butter mixture gradually and mix until barely incorporated. Add white chocolate and freeze dried raspberries and mix until just incorporated. Refrigerate the dough for at least 20 minutes, or up to 3 days.
Using an cookie dough scoop (or your hands!) make 1.5-tablespoon sized balls and place on a lined baking sheet. Using fingertips, gently press down each ball to about ¾-inch thickness.
Bake until cookies are golden brown, about 13 to 16 minutes, rotating baking sheet halfway through. Transfer baking sheet to wire rack to cool.
Bakers frequently rely on standard white chocolate baking chips that contain palm kernel oil instead of cocoa butter, which prevents them from melting smoothly and imparts a waxy mouthfeel to the finished pastry. Selecting a quality baking bar made with real cocoa butter provides superior melting characteristics and a richer flavor profile that balances the tartness of dehydrated fruit. Incorporating freeze-dried berries rather than fresh fruit prevents excess moisture from destabilizing the structural integrity of the dough during the baking process.
Fats creamed with granulated and light brown sugars must reach a pale, aerated state before the egg and vanilla extract are introduced at room temperature. This mechanical incorporation of air works alongside baking powder and baking soda to encourage proper expansion in the oven. When combining the dry elements with the butter base, mixing only until barely incorporated prevents the gluten in the all-purpose flour from developing excessive elasticity, keeping the final crumb tender.
Chilling the shaped portions for at least 20 minutes solidifies the butter content, which slows the rate of outward spread and creates a thicker cookie with distinct textural contrast between crisp edges and a soft center. Flattening the chilled dough balls to three-quarters of an inch thickness prior to placing them in the 350-degree Fahrenheit environment ensures even heat penetration throughout baking. Rotating the baking sheet halfway through the 13 to 16 minute cooking duration compensates for hot spots typically found in standard residential ovens.
Allowing the baked items to rest briefly on the hot metal before transferring them to a wire rack lets the centers set without overcooking the bottoms. Raw dough stored in the refrigerator remains viable for up to three days, permitting bakers to portion fresh batches on demand without sacrificing structural quality. Cooled portions stored in an airtight container maintain their textural qualities for several days at room temperature.