Preheat the oven to 350 degrees F. Butter an 8-inch square baking pan and line with parchment paper leaving a 2-inch overhand on each side.

In the bowl of the standing mixer using the paddle attachment, cream together the butter and sugars until smooth. Add the egg and vanilla. Add the flour and salt and mix until just incorporated. Fold in 1/2 cup of the white chocolate chips, the almonds and pistachios. Transfer the batter to the prepared pan and sprinkle with the remaining chocolate chips.

Bake until the top is golden brown and a toothpick  inserted into the center comes out clean, about 40 to 45 minutes. Set the pan on a wire rack and allow to cool completely.

Using the parchment overhang, lift the cake from the pan and transfer to a cutting board. Cut into 16 squares.