Peel hard-boiled eggs, cut into halves. If you can, aim for the cut that will perfectly bisect the yolk and leave some egg white surrounding it on both halves. Remove yolks and put into a mixing bowl, set egg whites aside in the fridge. Totally unnecessary, but I rinse any excess yolk off my egg whites so they're pretty. If you do this, make sure to pat them dry with a paper towel. Add the onion, pickles, pepper, and butter to the yolks. Mash well to combine. Next, add the mayo and mustard. This is all about your preferred taste and consistency of the yolk mixture (it will firm up some in the fridge). I usually end up with about 1 T of mustard and 1/2 cup of mayo. Adjust the ratio/amounts of mayo and mustard to your taste that also gives the mixture the consistency you prefer. At room temp I like it creamy enough so it doesn't have a grainy feel from the yolks, but thick enough that a heaping spoonful will stick to a spoon. When you get everything where you want it, salt to taste. Always wait until the very end to salt. Spoon a heaping spoonful into each egg white half. Garnish with paprika. These are good immediately but even better after chilling and firming up in the fridge for about an hour.