Add cubed potatoes to a large, heavy bottomed pot. Fill with enough water to cover the potatoes, then add salt and bring to a boil. Cook uncovered until potatoes are tender, about 25-30 minutes.
Meanwhile, in a small saucepan, heat butter and 2 teaspoons of dijon mustard over low heat until the butter melts, about 5 minutes. Slowly swirl the butter in the pan until it foams and turns light brown, roughly another 2 minutes. Remove from heat. The butter will continue to brown as it cools. Keep warm.
Once the potatoes are cooked, turn stove down to its lowest heat. Drain the potatoes and return to the stove. Use a fork to remove the skin, if desired. Add half and half (or heavy cream) and mustard. Mash in the pot until smooth and creamy. Taste then adjust flavor and consistency according to your preference by adding salt, mustard, or half and half.
Serve potatoes warm, topped with mustard browned butter, fresh black pepper and herbs.