Peel the potatoes and cut into uniform chunks. Avoid super small pieces as they will absorb too much water and practically disintegrate while boiling.
Place the potatoes in a pot with cold water and 1 tbsp salt. The water should be about two inches higher than the potatoes.
Boil the potatoes for 15-20 minutes. The time can vary, so you want to boil them until you can easily pierce them with a fork or the tip of a sharp knife. Overcooking will lead to mush and undercooking will lead to lumps, so be sure to check often.
Near the end of the cooking time, warm the heavy cream. I do this in a microwave safe dish in the microwave. You can also gently warm - but do not boil - the cream in a saucepan on the stove.
The tool you use to make your mashed potatoes will depend on the texture you want. I prefer my mashed potatoes to be really smooth, so I use a stand mixer with the paddle attachment. A hand mixer will work for this as well. If you prefer more texture, you can use a hand masher.
Place the cut potatoes in a mixing bowl.
Cut the butter into cubes and add it to the potatoes.
Mix on low speed until the butter melts.
Add in the warmed cream in a slow stream. You can add a bit, mix, and add more until you achieve the texture you prefer.
Crumble the Boursin and add to the potato mixture.
Mix on low speed until completely incorporated.
Salt to taste.