Preheat oven to 350 and line a 9 inch square pan with parchment paper.
Combine the dry ingredients (flour, powder, soda and salt) and set aside.
Crack open the eggs and combine with the vanilla in a small bowl.
Place the butter and sugars in a mixing bowl.
Place all of the caramel ingredients in a medium-sized, heavy-bottomed saucepan and set aside.
With a paddle attachment, cream the butter and sugar together until light and fluffy
Add in the egg mixture and mix until smooth.
Slowly add in the dry ingredients, mixing just to combine.
Turn the heat on to medium low and stir constantly while the butter and sugar melt.
Once melted, turn the heat up to medium high, stirring often.
Bring the mixture to 235F or until it's thickened and is a medium caramel brown. (I measured the temperature with an instant read thermometer because the caramel isn't deep enough for a candy thermometer).
Take the caramel off the heat and let cool for a minute.
Place half of the dough in the baking pan and smooth with an offset spatula.
Pour half of the caramel in the baking pan.
Scatter the white chocolate on top of the caramel (be careful the caramel will still be very hot).
Dot the pan with spoonfuls of the remaining dough.
Pour remaining caramel on top.
Sprinkle the cashew halves onto the caramel.
Using a measuring cup, press the top of the blondies to even out the dough.
Place the baking pan in the bottom rack of the oven and bake for 45-50 minutes or until the center no longer jiggles when you shake the pan.
Order is very important for these blondies...if you place the white chocolate or caramel on top they are likely to burn.
These blondies are the start to an awesome sundae! You can make an extra batch (or two) of salted caramel sauce to serve with blondies and vanilla ice cream.
To make the caramel sauce more stable for sundaes, add a pinch of baking soda after the sauce has reached 235F. The sauce will bubble up again, so be careful! This should keep the caramel from separating.