Prepare the Rosemary Hot Honey: Combine honey, chile slices, and rosemary sprig in a small saucepan; bring to a simmer over medium-low. Reduce heat to low, and cook until flavors have infused, about 1 hour. Pour through a fine wire-mesh strainer, and discard solids. Keep at room temperature until ready to use.
Prepare the Fried Chicken: Combine buttermilk, garlic, celery seeds, black pepper, and 4 teaspoons of the salt in a shallow dish; add chicken thighs, and rub to coat. Cover and marinate in refrigerator 4 hours, turning occasionally.
Combine flour, paprika, and remaining 1 teaspoon salt in a separate shallow dish. Remove chicken from marinade; discard remaining marinade. Dredge chicken in flour mixture, shaking off excess. Place chicken on a plate.
Heat oil to 325°F in a large cast-iron skillet or Dutch oven. Add chicken, in batches, and cook until deep golden brown and crisp and a thermometer inserted into thickest portion of chicken registers 165°F, 15 to 17 minutes. Transfer chicken to a plate lined with paper towels.
Prepare the Biscuits: Preheat oven to 450°F. Place butter and 1 tablespoon Rosemary Hot Honey in an 8- x 8-inch microwave-safe baking dish. Microwave on HIGH until butter melts, about 90 seconds. Combine flour and baking powder in a medium bowl; add buttermilk, and stir until a loose dough forms. (Batter will be a bit sticky.) Transfer dough to prepared baking dish, spreading evenly with a knife or the back of a spoon. (Butter will run over the top of the dough.) Score biscuit dough to make 9 squares. Bake in preheated oven until golden brown and top springs back when touched, 20 to 25 minutes. Cut into squares, and serve with Fried Chicken and remaining Rosemary Hot Honey.