Begin by wiping the mushrooms clean with a paper towel to remove any dirt; avoid rinsing them to prevent excess moisture. Slice or chop the mushrooms into uniform pieces, no thicker than 3 mm.

In a large shallow pan, heat 2 tablespoons of vegetable oil and 2 tablespoons of butter over medium-high heat. Once the butter has melted and begins to bubble, add the sliced mushrooms. Sauté the mushrooms for about 10 minutes, stirring occasionally.

Once the mushrooms are browned, stir in ½ teaspoon of fine sea salt, ¼ teaspoon of white pepper, and 1 teaspoon of onion granules, along with 1 tablespoon of soy sauce. Mix well to combine.

Pour in 1 cup of hot water and stir well. Allow the mixture to come to a gentle simmer over medium heat, stirring occasionally for about 2 minutes.

In a separate bowl, whisk together 1 cup of sour cream and 1 tablespoon of all-purpose flour, followed by a splash of cold water until smooth. Add a few tablespoons of the simmering pan sauce to it.

Carefully pour the tempered sour cream mixture into the pan with the mushroom sauce, stirring immediately to mix thoroughly. Cook over medium heat for another 1 to 2 minutes.

Season your Simple Mushroom Sauce with Sour Cream to taste, adding additional salt or pepper if needed. Remove from heat and serve immediately, garnishing with freshly chopped parsley.