Shepard's Pie

This recipe is from Everyday Food November 2007. Very simple and delicious recipe.
1 pound ground beef chuck
1 medium onion, chopped
1 garlic clove, minced
1/4 teaspoon dried thyme
2 tablespoons ketchup
1 tablespoon all-purpose flour
1 box (10 ounces) frozen mixed vegetables (no need to thaw)
Coarse salt and ground pepper
3 cups mashed potatoes
Directions
Preheat oven to 425 degrees. Heat a large (5-quart) heavy pot or Dutch oven over high. Cook beef, breaking up meat with a spoon, until no longer pink, 4 to 5 minutes. Add onion and garlic; cook until softened, about 4 minutes.
Add thyme, ketchup, and flour; stir until combined. Add 1/2 cup water and vegetables. Cook until vegetables are warmed through and liquid has thickened, about 3 minutes. Season with salt and pepper.
Spoon beef mixture into a 2-quart baking dish. Spread potatoes evenly over beef; using a fork, decorate potatoes with lines and peaks. Place dish on a rimmed baking sheet, and bake until potatoes are lightly browned, 10 to 15 minutes. Serve.