In a medium saucepan, melt the butter over medium heat until bubbly, about 2–3 minutes. Remove from heat and pour it over the white chocolate chips in a mixing bowl. Allow it to sit for 5 minutes, then whisk until smooth. Let sit for about 30 minutes to cool down to room temperature.

Once the butter-chocolate mixture has cooled, add granulated sugar, vanilla extract, and eggs to the bowl. Whisk until well combined and glossy.

Gently fold in the all-purpose flour and salt to the wet mixture until just combined. Then, delicately add in fresh blueberries, folding them in to maintain their shape.

Pour the batter into a lined 8x8-inch baking pan, spreading it evenly. Bake in a preheated oven at 350°F (175°C) for 35–45 minutes until the edges are golden brown and the center is slightly firm.

Once baked, allow the blondies to cool completely in the pan on a wire rack for about 1 hour. After cooling, slice into squares and serve.