Sauté the mushrooms in the fat (2 tablespoons) for five minutes in a skillet or saucepan over medium-high heat, or until much of the liquid from the mushrooms has evaporated. Don't stir too much, or the liquid won't evaporate as effectively.
Sprinkle the mushrooms with the flour (2 tablespoons) and stir to coat.
Add the broth/stock (2 cups) and stir until thickened (about 3 minutes).
Remove from heat and season with plenty of salt and pepper to taste.
Notes
For a gluten-free option, use cornstarch in place of flour.
For a grain-free/paleo option, use arrowroot powder or another grain-free thickener in place of flour.
The provided nutrition information does not include any added sodium from seasoning to taste, any optional ingredients, and it does not take brands into account. Feel free to calculate it yourself using this calculator or by adding the recipe to Yummly.