1 1/2 pounds Russet potatoes (about 3 large)
5 tablespoons olive oil or any neutral oil, such as canola, divided
2 (6- to 8-ounce) sirloin or boneless rib-eye steaks, approximately 1 to 1 1/4 inches thick, at room temperature
3 tablespoons unsalted butter, at room temperature
1 small shallot
1 medium lemon
Leaves of 3 to 4 sprigs fresh thyme
4 teaspoons kosher salt, divided
2 teaspoons coarsely ground black pepper