Preheat your oven to 350° F. Spray an 8x8 or 9x9 baking pan with non-stick spray and then line with parchment paper leaving overhand (for easy removal after). Set aside.
Melt the stick of butter in a large microwave-safe bowl in 30-second increments until fully melted. Add the brown sugar and mix with a spatula until fully combined. Add in the egg and vanilla and mix.
Add the flour, baking powder, and salt, and then mix until everything is combined. Mix in the white chocolate chips. Then fold in the raspberries gently, so that you don't break them (some will, which is fine). Make sure your raspberries are completely dry before adding them to the batter.
Pour the batter into the pan and gently spread it out. You can sprinkle a few extra raspberries and white chocolate chips on top if you would like (optional). Bake for about 30 minutes, until golden brown on the sides and the top. Leave them in the pan to cool completely and then cut into squares to serve.
You can double this recipe and make it in a 9x13 pan, or double and make it in a 9x9 but they will be chunkier. Add an additional 5-10 minutes to the baking time.
Make sure your raspberries are completely dry before adding them to the batter or else you'll get soggy blondies
Don't over mix the batter, this will lead to dense blondies and can sometimes lead to your blondies sinking in the middle.
Don't overcook the blondies or they will come out hard and dry. I usually check my blondies a few minutes before I think they're going to be done just in case.
When in doubt, use an oven thermometer to make sure your oven is at the correct temperature.