Preheat the oven to 400°F (200°C).

Rinse the chicken and pat dry; remove any excess fat. Season generously with sea salt and freshly ground black pepper inside and out.

Place the halved onion and rosemary sprigs inside the chicken cavity. Rub the outside of the chicken with the ground hot Hungarian paprika.

Lay a standard brown paper grocery bag on its side and place the prepared chicken inside. Tie the top of the bag closed with kitchen string.

Place the bagged chicken on a rimmed baking sheet in the lower third of the oven so there is room above it. Roast for about 1 1/2 hours (90 minutes).

Carefully open the bag to release steam. Check doneness by inserting an instant-read thermometer into the thickest part of the thigh; it should read about 165°F (74°C).

Let the chicken rest for about 10 minutes before carving. Slice breasts and separate wings, legs, and thighs. Serve warm.