1 medium-large head of cauliflower, about 2 ¼ pounds, cut into florets (about 5 cups)
1 pound Yukon Gold potatoes, peeled and cut into 1-inch pieces
2 Tablespoons unsalted butter (optional, but makes them taste better)
½ teaspoon of sea salt or to taste
Place cauliflower, potatoes and a big pinch of kosher salt in a large pot and add enough water to come just below the top of the vegetables.
Bring to a boil over high heat and then lower to a simmer. Cook until tender, about 15 minutes.
Drain cauliflower and potatoes and transfer to the bowl of a food processor fitted with the metal blade. Add butter and salt and process until smooth. Taste for seasoning and serve immediately.