Combine the Champagne and Dijon mustard in a small saucepan.
Place the saucepan over medium heat and bring the mixture to a gentle simmer, whisking occasionally.
Reduce the heat to low once the Champagne mixture begins to simmer.
Stir in the heavy cream.
Simmer gently for 3 to 4 minutes until the sauce thickens slightly.
Add the unsalted butter and whisk until it has melted completely and the sauce is smooth.
Stir in the chopped fresh tarragon.
Season with kosher salt and freshly ground black pepper to taste.
Remove the saucepan from the heat.
Drizzle the warm sauce over grilled steak, roasted beef, or beef tenderloin and serve immediately.
Notes & Wine Advice
Serving Suggestions
Spoon the warm sauce over grilled ribeye, filet mignon, roast beef, or beef tenderloin. Complete the meal with roasted asparagus, green beans, mashed potatoes, or our White Wine Rosemary Potatoes. A crisp green salad provides a fresh contrast to the creamy sauce.
Recipe Notes
Use dry Champagne or another good-quality dry sparkling wine. Allow the wine and mustard to simmer before adding the cream, but keep the heat low afterward to prevent the sauce from separating. Whisk in the butter near the end to give the sauce a smooth, glossy finish.
Variations
Replace fresh tarragon with finely chopped chives or parsley for a milder herbal flavour. Add a minced shallot before the Champagne for extra savoury depth. For a thicker sauce, let the Champagne reduce for another two minutes before adding the cream. Brandy can replace a small portion of the Champagne for a richer variation.
Storage and Reheating
Store leftover sauce in an airtight container in the refrigerator for up to three days. Reheat it slowly in a small saucepan over low heat while whisking frequently. Do not let it boil because excessive heat can cause the cream and butter to separate.
Wine Advice
Serve the sauce with the same dry Champagne or sparkling wine used in its preparation. An unoaked Chardonnay is a suitable still-wine alternative, particularly when the sauce accompanies beef tenderloin or a delicately seasoned steak.