Beef Tenderloin Medallions with Potato Risotto

Name: Beef Tenderloin Medallions with Potato Risotto
Ingredients: 1 tablespoon butter; 1 cup finely chopped onion; 1 pound Yukon Gold potatoes, peeled, cut into 1/8-inch-thick slices, then 1/8-inch cubes; 1/8 teaspoon cayenne pepper; Coarse kosher salt; 1 1/2 cups (or more) low-salt chicken broth; 1/2 cup heavy whipping cream; 1/4 cup finely grated Parmesan cheese; 1/4 cup finely chopped fresh chives; 6 6-ounce beef tenderloin steaks (each 3/4 to 1 inch thick); 1 1/2 tablespoons chopped fresh thyme; 1 tablespoon (or more) olive oil