Gravy's better with earthy mushrooms and rosemary.
In a medium saucepan, melt 2 tbsp. butter over medium-high heat. Add the mushrooms, onion, garlic, and rosemary. Cook, stirring occasionally, until the vegetables soften and are golden in spots, about 6 minutes.
Add the wine and stir, scraping up any browned bits. Bring to a boil and cook until almost dry, about 3 minutes. Add the stock; bring back to a boil. Remove from the heat and cover to keep warm.
In another medium saucepan, melt the remaining 4 tbsp. butter over medium heat. Add the flour and cook, whisking constantly, until the mixture is golden brown and smooth, 6 to 8 minutes.
Ladle about 1/2 cup of the stock into the flour mixture, whisking to blend. Continue adding 1/2 cupfuls of stock, whisking between each addition, until you’ve used up about half the stock. Pour in the remaining stock. Bring to a simmer. Cook, stirring occasionally, until the gravy thickens, 25 to 30 minutes.
Off heat, stir in the soy sauce; season to taste with salt and pepper. Strain the gravy (reserve the mushrooms for another use) or leave the gravy chunky.
