Hovmästarsås

Combine the mustard, sugar, vinegar, salt, and white pepper in a medium bowl. Whisk vigorously until the sugar has fully dissolved and the mixture is smooth and uniform. The mustard acts as both the flavor base and the emulsifier for the oil that follows — its natural lecithins will hold the sauce together. Taste this base before adding oil: it should be bracingly sharp and sweet in equal measure, with a clean vinegar edge. This is the correct starting point; the oil will soften and round it. If the balance seems wrong, adjust now — add more sugar if too sharp, more vinegar if too flat. The Swedish tradition calls for a sweeter sauce than French-style, leaning toward the balance you'd find in a honey mustard rather than a Dijon vinaigrette.

With one hand whisking constantly in tight circles, drizzle the neutral oil into the mustard base in a very thin, steady stream — start with drops, then increase to a thin trickle as the emulsion forms and strengthens. The sauce will thicken progressively as the oil is incorporated, shifting from a thin, sharp paste to a creamy, mayonnaise-like consistency. The mustard's emulsifying power is substantial, so this sauce is more forgiving than a true vinaigrette, but adding oil too fast will still break it. Once all the oil is incorporated and the sauce is glossy and thick, fold in the freshly chopped dill. The dill must go in at the very end — it will bleed its chlorophyll and color into the sauce if stirred in too early, turning it an unappetizing green-grey. The finished sauce should be pale gold-yellow with bright green dill flecks throughout. Refrigerate for at least 15 minutes before serving to let the flavors marry and the dill perfume to bloom fully.