Basic "brine": 1 cup sugar (or equivalent), 2/3 cup vinegar (I use ACV), 1 tsp salt - heat until sugar dissolves. No need to boil.
Then add seasonings while mixture is still hot. For dill, use dill seed (obviously). For bread & butter, use whole allspice, clove, little bit of stick cinnamon (I like more clove than cinnamon). Basically, it's like Justin Wilson's Cajun cooking: use what you like and what you got.
Slice your cukes (and onion) into the cooled mixture, put in fridge in glass container (Mason jar), and let rest 12 hours.