Place the chicken into a 4-quart or larger slow cooker. In a small bowl, whisk together the buffalo sauce, cornstarch and pepper. Pour this mixture over the chicken. Cut the butter into 2 pieces and place on top of chicken.
Cover and cook on LOW for 5 hours.
Shred the chicken with two forks.
Use tongs to get the chicken out of the slow cooker, tap the tongs on the side of the slow cooker to get the excess sauce off the chicken.
Place about a 1/2 cup of chicken into each tortilla and top with a heaping 1/8 cup of cheese.
Roll up the tortillas around the filling and secure with a toothpick. Note- If your tortillas start to crack while rolling them up. Wrap them in moist paper towels (before filling them) and microwave for 25 seconds.
Place the flautas onto a baking pan that has been sprayed with non-stick cooking spray.
Baste the flautas with the melted butter.
Preheat the oven to 425 degrees.
Cook the flautas for about 7 minutes, flipping once, and cooking for an additional 7 minutes or until golden brown.
Serve with ranch or blue cheese dressing.