In a large soup pot, cover the potatoes with cold water and bring to a boil.
Let cook until the potatoes are fork-tender, then remove from heat and rinse with cold water. Drain again.
While the potatoes are cooking (or cooling), brown the butter. In a heavy saute pan over medium heat, melt the butter. Stir occasionally, scraping the bottom of the pan, and bring the butter to a simmer. It should fizzle and pop. Continue to stir occasionally. Once the popping has died down, keep an eye on the solids in the pan: we want them to be a dark golden brown, but not to burn. Once they are golden brown, remove from heat and pour in with the potatoes.
Add the mascarpone, and mash the potatoes either with a masher or a hand mixer, to your desired consistency. Add cream as needed for thinning (I used only ¼ cup).
Add salt and pepper to taste (I used at least ½ tsp of each).
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/brown-butter-mascarpone-mashed-potatoes/