1. Position 1 oven rack on the highest setting. Position another rack on the lowest setting.
2. Preheat oven to 450°.
3. Arrange potatoes in a single layer on baking sheets. Coat with cooking spray; sprinkle with 1/4 teaspoon kosher salt. Bake at 450° for 40 minutes or until golden brown, stirring potatoes and rotating pans halfway through. Toss potatoes with 1 teaspoon thyme.
4. Heat a 12-inch heavy nonstick skillet over medium-high heat. Coat pan with cooking spray. Sprinkle both sides of steak with 1/4 teaspoon kosher salt and 1/4 teaspoon black pepper. Add steak to pan; sauté 3 minutes on each side or until desired degree of doneness. Remove from pan; keep steak warm.
5. Add shallots to pan; sauté 2 minutes. Add brandy; bring to a boil, scraping pan to loosen browned bits. Add beef broth, Dijon mustard, and remaining 1 teaspoon thyme; bring to a boil. Cook until reduced to 2/3 cup (about 3 minutes). Add remaining 1/4 teaspoon kosher salt and remaining 1/4 teaspoon black pepper. Add butter, stirring with a whisk.
6. Slice steak. Serve with shallot pan reduction sauce and potatoes.
Wine note: This classic dish deserves its classic match: cabernet sauvignon. If price is no object, opt for a top red Bordeaux from France. But to stay under $30, a rich, full-bodied cabernet from California will do the trick. The Geyser Peak Cabernet Sauvignon 2005 is a steal at just $18. —Karen MacNeil