Place potatoes in a large pot and bring to a boil and allow to simmer until the potatoes are done. This should take about 15 minutes. The potatoes should be fork tender.
Drain and run water over the potatoes to allow them to cool a little.
In a medium bowl add the olive oil, balsamic, lemon juice, salt, pepper, dill, parsley and onions and whisk to combine.
Add still warm potatoes to bowl and toss with the dressing, and herbs. Test for seasoning and adjust to taste. Sprinkle with crumbled feta if you wish and serve room temperature or cold.
Notes
On the potatoes - I like Yukon gold, but you can use red potatoes too. Don't pick starchy potatoes (russet) as they fall apart easier. I like to keep the peel on, but that is up to you.You can use red onion or a shallot - either works.Make it ahead -- it refrigerates very well for 3-4 days. Don't freeze -- potatoes will become mushy.Make sure to dress the potatoes while they are warm - they soak up much more flavor this way.