In a large bowl, combine buttermilk, rosemary, shallots, garlic, kosher salt, and sugar.
Add chicken and stir to fully coat. Allow to marinate for at least 4 hours or overnight for best results.
In a shallow dish, combine flour, smoked paprika, salt, and pepper.
Working with one piece at a time, remove chicken from buttermilk and shake off excess liquid.
Add to flour mixture and turn to coat evenly.
Shake off excess flour and dip the chicken in buttermilk.
Add again to flour mixture to fully coat.
In a thick-bottomed Dutch oven or cast-iron skillet, heat oil to 350 F.
Gently add chicken and deep-fry, turning once, until golden brown and crisp. DO NOT overcrowd the skillet, fry in batches as needed.
Remove chicken from the skillet and arrange in a single layer on a baking rack set onto a baking pan. Sprinkle with additional salt, if desired.
Bake in a 350 F oven for about 8 t 10 minutes or until a thermometer inserted into the thickest part of the chicken reads 165 F. Serve hot.