Slow-Roasted Beef Tenderloin

Name: Slow-Roasted Beef Tenderloin
Prep time: 10 min
Cook time: 190 min
Total time: 200 min
Yield: 6
Ingredients: 1 center-cut trimmed beef tenderloin, 2 to 3 pounds (900g to 1.4kg; see note); Kosher salt and freshly ground black pepper; 4 tablespoons (57g) unsalted butter; 4 sprigs thyme; 1 shallot, roughly sliced; Finely minced chives, for serving; Coarse sea salt, such as fleur de sel or Maldon, for serving; 1 recipe Horseradish Cream Sauce , for serving