In a large saucepan, heat the sour cream over medium heat until it begins to bubble gently.
Gradually whisk in the flour, stirring continuously to avoid lumps.
Cook the mixture for about 5-7 minutes, stirring frequently, until it thickens and starts to pull away from the sides of the pan.
Slowly add the milk, a little at a time, stirring continuously to keep the mixture smooth.
Continue to cook the mixture over medium heat, stirring frequently, until it reaches a creamy, porridge-like consistency. This should take about 10-15 minutes.
Stir in the butter and salt until the butter is melted and incorporated.
Enjoy your meal!