Ready in 45 minutes
1) Place the eggs into a saucepan in a single layer and fill with water to cover the eggs by 1 inch. Cover the saucepan and bring the water to a boil over high heat. Once the water is boiling, remove from the heat and let the eggs stand in the hot water for 15 minutes. Pour out the hot water, then cool the eggs under cold running water in the sink. Peel once cold.
2) Place the potatoes into a large pot and cover with salted water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Drain and allow to steam dry for a minute or two. Rinse the potatoes in cold water, and allow to cool. Slice the cooled potatoes into a large salad bowl.
3) Chop 2 hard-cooked eggs into the bowl with the potatoes, and mix in the celery, radishes, green pepper, and green onion. Stir together the cottage cheese and mayonnaise in a bowl, and pour over the potato mixture. Toss lightly to combine, and season to taste with salt and pepper. Slice the remaining hard-cooked egg, arrange the slices on top of the salad for a garnish, and sprinkle with black olives.