Peel, chop, and rinse potatoes. Fill water to just above the potatoes and add 1 tbsp salt. Bring to a boil and cook for about 20 minutes or until the potatoes are soft enough to fall apart when a knife is inserted in them.
Drain potatoes, and add 1/4 cup butter to the pot the potatoes were boiling in. Add the potatoes back to the pot then add fresh parsley, dill, and green onions followed by feta cheese. Place a lid on top of the potatoes and let them sit for 5 minutes.
Add black pepper to the potatoes and mash using a hand-mixer. Add milk if needed (one tablespoon at a time or until moist). Top with more fresh herbs and butter and serve immediately.