A good dollop of this on a serving of salmon is a treat.

I'm guesstimating quantities here, it all depends on number of servings are being made, usually I just start out with equal parts mayo to sour cream, then add the rest.  It's strong enough to stand up to a strong flavor like salmon, but doesn't overpower.

1/4 c mayo

1/4 c sour cream

dried or fresh dill to taste (we like a lot)

1/2 t dry mustard (more to taste but go carefully)

Mix up the night before or at least several hours early so the dry mustard has a chance to develop … start slow with dry mustard, it develops in flavor so don't taste it as you mix it and add more without waiting a bit. 

Dry mustard really adds depth to a creamy recipe like this.