Move the oven racks to the upper middle and lower middle positions. Preheat oven to 250 degrees F. Line a baking sheet with foil, and place a wire rack on top. Spray the wire rack lightly with nonstick cooking spray; set aside.
PREP AND BAKE THE CHICKEN WINGS:
Pat the thawed chicken wings dry with paper towels.
Place the chicken wings in a gallon-sized Ziploc bag. Add the baking powder and salt and seal the bag shut. Shake the bag until each wing is coated with baking powder.
Remove the chicken wings from the bag and place them, skin-side up, on top of the wire rack on your prepared baking sheet.
Place the baking sheet on the lower-middle rack and bake for 30 minutes. Move wings to upper-middle rack and increase oven temperature to 425 degrees F. Bake an additional 40-50 minutes, or until wings are crispy and golden-brown. Remove the wings from the oven and cool for 5 minutes.
MAKE THE DR PEPPER WING SAUCE:
While the wings are in the oven, make the wing sauce by adding Dr. Pepper, Buffalo wing sauce, and brown sugar to a medium saucepan. Heat over high heat until mixture comes to a boil. Continue to boil for 5 minutes, whisking every minute or so. Reduce heat until mixture reaches a low boil. Continue to cook for 15-20 minutes (stirring occasionally) until the mixture reduces by half.
Add in the butter and whisk until melted.
Add in the cornstarch and continue to boil until thickened, about 2-3 minutes.
Turn off the heat and let the sauce sit for 5 minutes. Add the wings to a large bowl. Pour sauce over, toss until well coated, and serve immediately!