Heat the oven to 375°F. Line a small baking sheet with parchment paper.
In a large mixing bowl, stir together the mashed potatoes, egg, celery, onion, ¼ cup of the Buffalo sauce, garlic powder, salt, and black pepper.
Add the ground turkey and ¼ cup of the blue cheese. Mix gently with clean hands or a fork just until combined. Avoid overmixing so the meatloaf stays tender.
Shape the mixture into a compact loaf on the prepared baking sheet. Spread the remaining Buffalo sauce over the top.
Bake until the center reaches 165°F on an instant-read thermometer, about 45 to 55 minutes. Sprinkle the remaining blue cheese over the top during the last 5 minutes of baking.
Let the meatloaf rest for 10 minutes before slicing. This helps the slices hold their shape.