Preheat the oven to 400°. Spray a sheet pan with baking spray and top with a cooling rack or similar; spray tray with baking spray as well.
With a fork, stir together in a large bowl the ground chicken or turkey, onion, garlic, egg white, panko crumbs and Ranch dip mix until just combined. Divide mixture into 16 equal portions.
Make a well in the center of a meatball and add about 1/2 Tbsp of crumbled blue cheese. Form the meatball around the blue cheese and pinch ends to seal. Roll into a ball. Place meatball on the cooling rack. Repeat until all 16 meatballs have been stuffed and formed.
Bake meatballs for 18-22 minutes, rotating sheet pan once through baking time, until meatballs are cooked through.
Meanwhile, melt butter in a large non-stick skillet over medium heat. Then add buffalo wing sauce and stir to combine. When baked, add meatballs to the buffalo sauce mixture and roll in the sauce, using a spoon to make sure meatballs are well coated. Cover the skillet with a lid and turn heat to low to keep meatballs warm.
If you are making this for a crowd, you can use your slow cooker to sauce the meatballs and keep them warm while serving. Simply add the meatballs to the warmed slow cooker, pour sauce mixture over and stir to coat.
Serve as-is or with your favorite "buffalo wing" sides, such as carrots and celery sticks with Ranch or blue cheese dressing for dipping.