Preheat the oven to 350 degrees F.
Cook the pasta according to the package directions for al dente. Drain and set aside.
In a large saucepan over medium heat, melt the butter.
Whisk in the flour, then add the onion powder, salt, and pepper. Gradually whisk in the milk.
Cook, stirring constantly, until the sauce thickens and the mixture begins to boil.
Add the cheese and stir until melted. Add the pasta and stir to coat.
Pour into a 9x13-inch baking dish.
Mix together the crushed Ritz crackers and melted butter and sprinkle over the top.
Bake for 30 minutes, until golden and bubbly.
Let stand for 10 minutes and serve.
