Place potatoes in a large stockpot with enough cold water to cover.

Bring stockpot to a boil and allow potatoes to cook for about 20 minutes until very tender and able to be pierced easily with a fork.

Drain water from potatoes and return to stockpot.

While the potatoes are still hot, add the champagne, heavy cream, salt and butter.

Using an immersion blender, mash and blend the potatoes until smooth.

With a large spoon, stir in the diced Havarti cheese into the mashed potatoes until melted, then mix in the tarragon and thyme.

At this point, if you feel your potatoes seem a little too dry, you can add another tablespoon of butter and a splash more of champagne.

Place the mashed potatoes into a serving bowl, sprinkle with a bit of pink sea salt and some chopped thyme and serve immediately