In a shallow dish, stir together buttermilk, 4 teaspoons salt, and pepper. Add chicken, tossing to coat. Cover and refrigerate for at least 4 hours or overnight, turning occasionally.

In a small saucepan, bring honey, hot sauce, red pepper, and rosemary to a simmer over medium-low heat. Reduce heat to low; cook for 1 hour. Pour mixture through a fine-mesh sieve, discarding solids. Cover and let stand at room temperature until ready to use.

In another shallow dish, combine flour, paprika, and remaining 1 teaspoon salt. Remove chicken from dish, discarding marinade. Dredge chicken in flour mixture, shaking off excess. Place chicken on a plate; let stand for 10 minutes.

In a large cast-iron skillet or Dutch oven, pour oil to a depth of 2 inches, and heat over medium heat until a deep-fry thermometer registers 350°.

Working in batches, fry chicken until deep golden brown and crispy and a meat thermometer inserted in thickest portion registers 165°, 15 to 17 minutes. Transfer chicken to a wire rack to drain.

Cut Buttermilk Biscuits in half. Place chicken halves on bottom half of biscuits, and top with spicy honey. Cover with biscuit tops. Garnish with rosemary, if desired.