Add the potatoes to a large pot and cover them with 3 to 4 inches of water. Add 1 ½ teaspoons of salt and stir. Bring the water and potatoes to a boil over high heat.
Once boiling, reduce the heat to medium and keep boiling them until they're fork-tender, about 17 to 20 minutes. They should break up in half easily. When they're ready, drain the water and place the potatoes back in the pot.
Make them creamy:
Blend the cottage cheese for a full minute, until it's whipped and smooth.
To the potatoes in the pot, add the butter, 1 teaspoon salt, and pepper. Use a potato masher and start mashing the potatoes, add the milk, and keep mashing. You can also use a hand mixer to mash and whip the potatoes. Towards the end, when you've achieved the mashed-potato mixture you like, add the whipped cottage cheese to the pot. Use a large spoon or spatula to combine the cottage cheese with the mashed potatoes.
Tip: if the mashed potatoes have started to get cold because the cottage cheese isn't warm, turn the heat to the lowest setting to warm it up just enough.