Creamy, Dreamy Stovetop Macaroni & Cheese

This is my husbands favorite Mac and Cheese because it remains nice and moist (and rich!)

Ingredients:

• 3 tablespoons unsalted butter
• 1/4 cup finely chopped onion
• 1/3 cup all-purpose flour
• Coarse salt & Pepper
• 4 cups whole milk
• 1/8 teaspoon cayenne pepper (optional)
• 3/4 pound small shell pasta or elbow macaroni
• 4 cups coarsely grated sharp yellow cheddar (3/4 pound)

• 1 teaspoon Mustard powder
• 1 teaspoon Worcestershire sauce
• Directions:
• In a medium saucepan, melt butter over medium; add onion and cook until softened, about 4 minutes. Add flour and 1/2 teaspoon salt; cook, stirring frequently, until mixture is pale golden, has a slightly nutty aroma, and is the texture of cooked oatmeal, about 5 minutes. 
• Whisking constantly, pour in 2 cups milk; add 2 more cups milk, mustard powder, and cayenne (if using) and whisk until smooth. Cook mixture, stirring constantly along bottom of pan, until boiling, 6 to 7 minutes. Reduce heat to low. Simmer gently, stirring occasionally, until sauce thickens and doesn't look grainy. 
• Meanwhile in a large pot of boiling salted water, cook pasta until al dente, drain and return to the pot. Remove from heat and let cool a minute, then quickly stir in cheese and Worcestershire Sauce. Pour cheese over the pasta, and stir until it's coated. Enjoy!