Sous Proven'Cal

This sauce starts like a classic handmade mayonnaise: egg yolks, mustard, vinegar, and olive oil beaten together drop by drop until thick and emulsified. Then it goes somewhere entirely different. Stiffly whipped egg whites get folded in for volume and lightness, followed by sour cream or yogurt for tang.

The result is something between a mousse and a cold sauce. Lighter than straight mayonnaise, tangier than aioli, and with an airy texture from those whipped whites that you don’t find in any store-bought condiment.

The drop-by-drop oil addition is the step that can’t be rushed. Adding oil too fast breaks the emulsion and you end up with a greasy, split mess instead of a thick, glossy base. Patience here pays off.

Pro Tips

• Have all ingredients at room temperature before starting. Cold yolks emulsify poorly and cold egg whites won’t whip to stiff peaks.
• Beat the oil in literally one drop at a time for the first tablespoon or two. Once the emulsion catches and thickens, you can increase to a thin, steady stream.
• Fold the whipped whites in gently with a spatula, not a whisk. You spent time building that volume, and aggressive stirring deflates it.
• The 2 to 4 hour chill is key. It firms the sauce, melds the flavors, and lets the vinegar and mustard notes settle into the cream.

Variations

• Use Greek yogurt instead of sour cream for an even tangier, thicker result.
• Add a crushed clove of garlic to the yolk mixture for a Provencal aioli-style variation.
• Stir in chopped fresh tarragon or chives after folding in the whites for an herbed version that pairs well with cold fish.