Peel and finely chop the onion. Dilute vinegar and boil down with peppercorns and onion, then strain.
Whisk the yolks in the cold beef broth. Heat a pot of water and whisk the yolk mixture in the water bath until the mixture is creamy.
Melt butter and drizzle into yolk mixture alternately with strained onion mixture.
Season hollandaise sauce with lemon juice and salt.