Take grouse from the fridge, let sit for 30 minutes, and preheat the oven to 450℉.
Take ½ tablespoon of butter and stuff it into the crop of the grouse and take the other ½ tablespoon and smear it all over the bird. Do not add salt to the bird, as it's already seasoned from the brine.
Cut 2 slices of orange in half so they fit better into the bird’s cavity, and stuff them into the inside of the grouse along with 2 sprigs of rosemary.
Truss the bird with some kitchen string.
Place the bird into a cast iron pan or roasting pan, cut the remaining orange slices in half, and arrange them around the bird along with the last 2 springs of rosemary and the pomegranate seeds.
Roast for 20 minutes, then reduce oven to 350℉ and continue roasting for another 10 minutes. You are looking for a temperature of 150 to 155℉. Size of birds vary, so adjust the time to suit bird size.
During the last 10 minutes of cooking, brush on the pomegranate glaze a few times.
Remove from oven and let rest for 5 to 10 minutes.
Carve like a chicken and place pieces in a serving plate topped with the roasted oranges and pomegranate seeds, fresh pomegranate seeds, and whatever juices are left in the pan. Serve with whatever sides you prefer. I suggest roasted potatoes.