From Bon Appetite
1 pound Jerusalem artichokes unpeeled, scrubbed, cut into 1-1 ½ inch pieces
1 pound russet potatoes, peeled, cut into 2-inch pieces
1 tbsp coarse kosher salt
3 tbsp butter
Combine artichokes and potatoes in a large pot. Pour enough cold water to cover; add 1 tbsp coarse kosher salt. Bring to a boil; reduce heat and boil gently until al vegetables are tender when pierced with a knife about 18 minutes. Drain, reserving cooking liquid. Return vegetables to pot. Mash, adding reserved cooking liquid by ½ cupfuls to moisten until chunky mixture forms. Stir in butter. Season to taste with salt and pepper.