TO MAKE THE APPLE BROWN BUTTER BATTER:
Cook butter in a medium saucepan over medium heat, stirring often, until butter foams, then browns, 5–8 minutes.
Transfer brown butter to a medium bowl; let cool slightly.
Add the apple butter, egg, brown sugar, vanilla, and salt and beat for about 3 minutes until silky smooth.
Fold in the All-Purpose Flour Artisan Blend.
TO MAKE THE BLONDIE BATTER:
Preheat oven to 350°F. Butter a 12x8x2 baking pan and dust with Pamela's gluten free all purpose flour. Toast the pecans on a baking sheet, tossing once, until golden and fragrant, 8–10 minutes. Let cool.
Whisk the baking powder, salt, and 2¼ cups Pamela's gluten free all purpose flour in a medium bowl. Using an electric mixer on medium-high speed, beat the dark brown sugar and 1 cup butter in a large bowl until light and fluffy, about 5 minutes. Add eggs one at a time, beating between additions; mix until pale and fluffy, about 2 minutes. Mix in vanilla.
Reduce speed to low and mix in dry ingredients. Fold in half of the pecans then scrape two-thirds of the batter into the prepared baking dish; smooth the top, pushing the batter to the edges. Alternate dropping dollops of the apple brown butter mixture and remaining batter on top. Smooth and sprinkle the remaining pecans over.
Bake until the blondie is golden brown and firm (a tester will not come out clean), 45-50 minutes. Let cool before slicing. Serve with ice cream.
Don't own a 12x8x2" baking pan? Simply use a 13x9" baking dish instead and shorten the cooking time to 35-40 minutes since the brownies will be thinner.