Cook the pasta: 1. Boil water in a large pot and add salt. 2. Cook the pasta until al dente following package instructions. 3. Drain and set aside.

Prepare the white sauce: 1. In a separate saucepan, melt butter over medium heat. 2. Add minced garlic and sauté until fragrant. 3. Add chopped onions and cook until they become translucent. 4. Gradually whisk in all-purpose flour to form a roux. 5. Cook the roux for a minute or two to remove the raw flour taste.

Cook the white sauce: 1. Slowly pour in the milk while continuously whisking to avoid lumps. 2. Keep stirring until the sauce thickens and reaches a smooth, creamy consistency. 3. Season the sauce with salt, black pepper, and red chili flakes (if using). 4. Optional: Add grated Parmesan cheese to enhance the creaminess.

Add vegetables (optional): 1. If desired, add mixed vegetables like bell peppers, broccoli, or mushrooms to the sauce. 2. Cook until the vegetables are slightly tender.

Combine with pasta: 1. Add the cooked pasta to the white sauce. 2. Toss everything together until the pasta is evenly coated with the creamy sauce.

Final touches: 1. Adjust seasoning if needed. 2. Garnish with fresh parsley or basil leaves for a pop of color and flavor.