In large pot of boiling salted water, cook noodles according to package directions (approximately 10 – 12 minutes). Preheat oven to 350°F.
Meanwhile, melt butter in a small saucepan over medium heat. Add flour and stir until well combined. Add milk, stirring constantly as the mixture thickens.
Add cheddar cheese and salsa to milk and butter mixture. Drain pasta and add to cheese mixture, stirring to coat. Pour into a buttered baking dish and bake until browned and bubbly. This will be approximately 30 minutes.