Preheat the oven to 350°.
In a medium hot skillet or Dutch oven, toast the uncooked rice in 1 tsp olive oil for two minutes.
Add 2 tablespoons of butter and then the mushrooms. Cook three to four minutes, stirring two or three times.
Add 2 cups of hot chicken stock and the cranberries. It's especially important that the stock be hot if you're using cast iron. Cast iron can crack the same way glass does when you add hot to cold or cold to hot.
Bake at 350° for 30 minutes.
Fluff the rice. Nestle the grouse into the rice, add the walnuts, and return the cover. Continue to bake for an additional 20 minutes.