I found this recipe on Honest Fare about 5 years ago. This is the second time I've done this. They say cucumbers, but why not beans too?!? :)
6-8 pickling cucumbers
1 cup distilled white vinegar
1/4 cup white sugar (optional or use less if you don’t want any sweetness)
1 ½ Tablespoon salt
½ -1 teaspoon *red pepper flakes
1 teaspoon celery seed
1 Tablespoon mustard seed or stone ground mustard
1 ½ teaspoon horseradish
A LOT of dill (like 1/3 cup diced)
2 garlic cloves
¼ cup sliced **white onion
2-3 Tablespoons water
*I altered the recipe a bit by only adding the *red pepper flakes to the beans and using **purple onions instead, as that's all I had at the time.
Slice about ¼ of an onion into thin slivers. Peel and smash garlic
with your knife (but don’t chop or dice though). Put garlic and onion in
a pot with vinegar, sugar, salt, celery seed, red pepper flakes, splash
of water and half your dill. If you have mustard seed, you can add that
to the pot too. But if you’re using mustard powder or stone ground
mustard as an alternate, don’t add it yet.
Bring contents in pot to a nice simmer and then immediately turn off heat and let cool for about 10 minutes.
Add the remaining fresh dill and mustard or horseradish if you like.
Then put the lid on tight and give it a few nice shakes before storing
it in the fridge over night.
Give the jar a stern shake every few hours if you remember.