Mustard is a wonderful accompaniment to many things, and I’ve found that when added to this simple sauce recipe, it can really enhance other dishes. As a cream sauce, it provides for a gentle, yet savory coating for your meal.
In a medium saucepan over medium-high heat, combine sour cream and heavy cream, bring to a simmer. Cook, whisking constantly and adjusting heat as needed to maintain a simmer, until sauce is thick and coats the back of a spoon, 4 to 8 minutes.
Reduce heat to medium-low, stir in mustard and thyme and simmer, whisking constantly, for 2 minutes more.
If you prefer your sauce on the spicy side, or are planning on serving it with beef, consider stirring 1 tablespoon horseradish into the sauce for an added kick.