Place the well-scrubbed potatoes in a large fleishig pot and fill with cold water to 1 inch above the potatoes. Bring to a boil and stir in 1 tablespoon of salt. Cook uncovered for 30 to 45 minutes, or until a knife pierces through the potatoes.

Drain the potatoes in a colander and peel. Return to the pot and mash them using a ricer, food mill, or masher.

Stir in the coconut oil and pareve milk until incorporated. Mix in the pastrami, garlic, mayonnaise, rosemary, salt, and pepper. Serve warm.