Gently rinse and thoroughly dry the fresh blueberries.
Prepare a baking tray (approx. 9x13 inch or similar) by lining it with parchment paper.
Preheat oven to 170°C - 180°C (340°F - 355°F).
2. Mixing (Planetary Mixer - Standard Method):
Place the SwissBake Blondie Mix and the water in the mixing bowl.
Using a paddle attachment, mix at low speed for 1 minute.
Stop the mixer and scrape down the sides and bottom of the bowl to ensure all ingredients are incorporated.
Add the oil to the batter and mix again at low speed for 1 minute.
Perform a final scrape of the batter. Mix at medium speed for 3 to 4 minutes to develop the batter's structure.
Reduce to low speed and add the white chocolate cubes and fresh blueberries. Mix for 1 minute or only until the inclusions are evenly distributed. Do not overmix, as this can crush the blueberries and discolor the batter.
3. Panning & Assembly:
Pour the finished blondie batter into the baking tray lined with parchment paper.
Use an offset spatula to spread the batter evenly to all corners of the tray.
4. Baking:
Place the tray in the preheated oven.
Bake at 170°C to 180°C for 25-30 minutes.
The blondie is baked when the top is golden-brown, the edges are set, and a skewer inserted into the center comes out with moist crumbs attached (not wet batter).
5. Cooling:
Once baked, remove the tray from the oven.
Let it cool down completely in the tray on a wire rack before attempting to slice. This is crucial for achieving clean, fudgy squares.
Once cooled, lift the entire blondie out of the tray using the parchment paper and cut into desired portions.