My dad was in WWII and was a cook in the army. He was an awesome cook and one of the dishes he made for us that I loved were the delicious tender potatoes, my mom made them also. From what I remember here is my version of how they were prepared.
In a large skillet, melt the butter and 1 tablespoon of olive oil. Slice the onions and garlic and cook in the pan until tender.
While the onions are cooking, peel, wash and dry off potatoes, cut them in half and then make slices about 1/2" thick. Lay the potatoes on top of the onions, cover and cook on a low heat. The trick to these potatoes are to cook on a low heat covered and add a little bit of water at a time once the liquid is almost evaporated.
When you see the potatoes turn transparent, stir and add parsley, salt and pepper. Cover and continue to cook on low watching the liquid. Add a little bit of water and 2nd tablespoon of olive oil when the liquid is almost gone.
Keep the skillet covered, stirring occassionally. When the potatoes are tender, throw in about 1/4 cup of frozen peas (optional) and continue to cook about another 10 minutes or until the potatoes are nice and tender and at this point will have a nice gravy.