Lemon sauce can be used to accent both poultry and seafood. Change the spices in the sauce to accent different flavors. For example, add fresh thyme or rosemary when making lemon sauce for poultry.
Place a handful of fresh dill on a cutting board. Chop the dill finely by rocking a chef's knife back and forth over the herb. Push the dill into a pile and continue to chop until a fine consistency is met. Do not use dry dill as a substitute.
Squeeze the juice from one large lemon into a bowl. Squeeze the lemon over a sieve to catch any seeds and large pulp. Add the chopped dill to the lemon juice.
Mix in the mustard, soy sauce, salt and pepper. Start by adding the basic amount of each ingredient. Add more of each of the ingredients as desired. Go easy on the salt as soy sauce has a high sodium content.
Scoop the sour cream out of the container and add it to the lemon mixture. Use a wire whisk to combine all of the ingredients. Whisk the sauce until it is very smooth and contains no lumps of sour cream.
Bake the fish or poultry until it has reached a temperature safe for consuming. Place a portion of the meat on a serving plate. Spoon the lemon sauce over the top of the fish or poultry, and add a sprig of dill to each plate for garnish. Place a ramekin of lemon sauce on the side of each plate for dipping.