Heat up the water in a pot and add the salt and sugar. Stir until completely dissolved. Let the water cool down to at least room temperature, then add the whole grouse, ensuring they’re submerged in the water. Put the pot in the fridge and brine the grouse for 5-8 hours.
Add the raw rice, 1 tablespoon of butter, sliced sausage, giblets, scallions, and garlic to a pot over medium heat. Cook, stirring very often, for 5-10 minutes, or until the rice smells toasty and has become opaquely white, and the sausage has begun to render its fat.
Add the water and a pinch of salt, bring to a boil, cover, and reduce heat to low. Cook for 18 minutes without disturbing the lid, then let it rest off of the heat for 10 minutes.
Fluff with a fork and stir in the soy sauce.
Preheat oven to 475°F.
Stuff the rice mixture into the cavities of the birds. Rub ¼ cup of butter all over each bird. If the skin is still intact, be sure to rub some butter in under the skin, especially over the breasts. Season the exterior of the birds generously with salt and pepper.
Put the birds on a sheet pan fitted with a rack, or in an oven-proof skillet and put in the oven for 15 minutes. Turn the temperature down to 350°F and let the grouse cook for another 15-20 minutes, basting with any butter that has accumulated in the bottom of the skillet.
Remove the grouse from the oven, cover with foil, and let rest for 10 minutes before serving. Enjoy!
