Peel the russet potatoes and cut them into evenly sized chunks.
Place the potatoes in a large pot and cover with cold water.
Add a generous pinch of salt to the water.
Bring the water to a boil over medium-high heat.
Reduce heat and simmer for about 20 minutes or until the potatoes are tender.
Drain the potatoes well in a colander.
In the same pot, melt the butter over low heat.
Return the drained potatoes to the pot and mash them using a potato masher.
Gradually add the heavy cream while continuing to mash until smooth and creamy.
Season with salt and pepper to taste, and mix in any optional ingredients.