Applebee's Maple Blondie with Maple Buttercream Sauce

1/3 cup butter, melted
1 cup packed brown sugar
1 large egg
1/2 tablespoon vanilla extract
1/2 tablespoon maple extract
1 cup flour
1/4 teaspoon baking powder
1/2 teaspoon baking soda
pinch of sea salt
1/2 cup chopped walnuts
1/2 cup white chocolate chips
For the Maple Butter Cream Sauce:
1/2 cup butter, softened
1/2 cup powdered sugar
4 ounces cream cheese, softened
2 tablespoon maple syrup

Preheat the oven to 350ºF. Line an 8x8 or 9x9 baking dish with parchment paper (or line with foil and lightly grease).
Beat together the butter and brown sugar. Add the egg and vanilla extract, mix well.
Add the four, baking powder, baking soda, and salt. Mix well until batter forms.
Stir in the walnuts and the white chocolate chips.
Spread the batter in the baking dish. Bake for 25 minutes (the middle will still be slightly jiggly,
and there may still be a little batter on a toothpick when inserted).
Let cool for at least 10 minutes.
For the sauce:
Use a mixer or food processor to mix together the butter, cream cheese, powdered sugar,
and maple syrup (I use a small food processor to make sure I don't have any lumps!).
Pour sauce over the blondie* before serving (optional: you can heat this sauce for about 15 seconds in the microwave before serving if desired).

Notes

The sauce being poured over the ice cream in the pictures, but after extensive (ahem) taste testing,
it is better poured directly over the blondie with the ice cream on top of it all.

And if you're serving the blondie fresh out of the oven, there's really no need to heat the sauce at all, even if you want it warmed.
The high ratio of butter in the sauce will ensure that it gets all warm and melt-y once it hits the warm blondie.