Mustard Cream Sauce
A simple Velouté-based sauce that demonstrates the importance of tempering mustard to preserve its volatile heat — the defining sauce of "Senfeier" (Mustard Eggs), a beloved dish found in German school canteens and grandmothers' kitchens alike.
The technique hinges on one critical rule: mustard must be added last, after the heat is turned off. The compounds that give mustard its sinus-clearing kick — isothiocyanates — are extremely sensitive to heat. Boil them, and the sauce loses its brightness, developing a dull, bitter aftertaste. Instead, build a classic white sauce from roux, stock, and cream, simmer it until velvety smooth, then whisk in a generous measure of medium-hot German mustard (Mittelscharf) at the very last moment. The result is a sauce that is simultaneously comforting and piquant, its warmth perfectly complementing boiled eggs, poached fish, or simple steamed vegetables.
History & Origins
Mustard has been cultivated in Germany since the Roman times. This sauce became a staple during Lent and other meatless days, providing a protein-rich and flavor-packed experience through eggs and dairy rather than expensive cuts of meat.
The Science
Isothiocyanate Sensitivity. The heat in mustard comes from isothiocyanates. These compounds are very sensitive to high heat. If you boil the mustard for long, the sauce will lose its 'kick' and can develop a dull, bitter aftertaste.
Technique
The Final Temper. Build a classic white sauce (Roux + Stock + Cream) and simmer it until thick. Only at the very last second, after turning off the heat, whisk in the mustard. This preserves the brightness and the sinus-clearing 'pop' of the mustard.
Common Mistakes
Using only sweet mustard. While Bavarian sweet mustard is delicious, it doesn't provide the necessary acidity for this sauce. Always use a 'Mittelscharf' (medium-hot) German mustard, or a mix of Dijon and a little bit of sugar.
Chef's Notes
For a more gourmet version, add a few capers or a tiny bit of horseradish to the final whisk-in. It adds a whole new dimension of sharpness that pairs perfectly with poached fish.