In a small saucepan, melt butter over medium heat, stirring occasionally.
Once melted, let the butter continue to bubble away, carefully swirling the pan every 30 secs. Cook for 5 mins then transfer to a large bowl and cool for a few mins.
Meanwhile, arrange a rack in the centre of the oven and heat to 175ºC.
Grease an 8-x 8-inch baking pan. For easy blondie removal, you can also line with a strip of parchment.
Add the brown sugar to the cooled browned butter in the bowl and whisk to combine. Add the egg and vanilla, then whisk until well combined.
Add the flour, baking powder, and salt. Mix again, then add the nuts, 2 ounces of the chopped ruby chocolate, and half of the freeze-dried berries; stirring until combined.
Transfer the batter to the prepared pan, spreading into an even layer. Then, bake until the edges are set for about, 20 to 24 mins.
While the blondies are still hot, sprinkle evenly with the white chocolate and remaining ruby chocolate. Let the chocolate melt for a few minutes, then use an offset spatula or knife to spread and swirl, creating a marbled design.
Sprinkle evenly with the remaining crushed freeze-dried berries before the chocolate sets.
Cool to room temperature for at least an hour. If needed, move the cooled blondies to the fridge for a few minutes to help the chocolate set.