Prepare the peppers. Wash the peppers. Cut a lid around each stem and reserve the tops. Carefully remove the seeds and pale membranes without piercing the walls. Weigh the cleaned peppers to match the ingredient list; the number of pods varies with size.
Rinse rice and chop aromatics. Rinse the raw rice in a fine-mesh sieve until the water runs noticeably clearer, then drain thoroughly. Dice the onion into roughly ⅛-inch (3–4 mm) pieces and mince or press the garlic.
Briefly cook the tomato paste. Heat the sunflower oil in the wide pot over medium heat. Stir in the tomato paste and cook for about 1 minute without letting it darken or scorch.
Make the light sauce. Slowly stir in the passata and initial hot water. Add the sauce salt, sauce pepper, sugar, and bay leaves. Bring to a simmer, cook gently for 5 minutes, then temporarily take the pot off the heat.
Mix the raw filling. Combine the raw ground beef, drained raw rice, onion, garlic, egg, filling salt, filling pepper, and sweet paprika in a bowl. Mix with clean hands only until evenly distributed; do not knead into a dense paste. Wash hands, work surfaces, and utensils thoroughly after handling raw beef and egg.
Fill loosely. Distribute the mixture loosely among the prepared peppers, leaving about ⅜ inch (1 cm) below each rim. Do not compress the mixture: the rice needs space to expand. Replace the reserved pepper tops.
Arrange and check the level. Set the peppers close together and as upright as possible in the sauce. It should reach halfway to two-thirds up their height. Add some of the optional hot water only if needed for that level, without submerging or flooding the peppers.
Return to a gentle simmer. Cover and warm over medium heat, allowing about 10 minutes to return to a gentle simmer. Reduce to low heat so the sauce bubbles lightly rather than boiling hard.
Braise without stirring. Cook covered at a gentle simmer for 65–70 minutes. Do not stir between the peppers. If needed, carefully shift the covered pot by its handles to redistribute the liquid, without splashing or tilting it dangerously.
Check the sauce. After about 60 minutes of braising, check the liquid level. If the sauce is reducing enough to catch on the bottom, add a little hot water at the side of the pot. Keep the heat gentle and replace the lid.
Verify the filling. At about 65 minutes, check a particularly large pepper and other large pieces as needed. The rice must be fully tender, and the center of the beef filling must measure at least 160°F (71.1°C) with a clean thermometer. Do not rely on meat color, pepper softness, or a boiling sauce.
Continue if needed. If the rice is firm or the filling has not reached the safe temperature, cover and cook for another 10–15 minutes, then check again. Thick-walled or larger peppers can need longer; both checks must pass before resting.
Rest and serve. Remove the pot from the heat and rest, covered, for 10 minutes. Remove the bay leaves. Lift the peppers gently onto deep plates and divide the peppers and tomato sauce among the servings. Serve hot.