Brown beef and onion in a deep 12-inch saute pan over medium-high heat for 8 minutes, breaking it finely and cooking to 160°F. Drain excess fat and stir in garlic for 30 seconds.
Add tomatoes and chiles with their juices, cavatappi, broth, salt and pepper and bring to a simmer.
Cook uncovered over medium-low heat for 12 to 15 minutes, stirring every 2 minutes until pasta is tender. Add reserved water only as needed to prevent the sauce drying early.
Lower the heat and stir in milk and cream cheese a few pieces at a time until fully melted, about 2 minutes, without boiling hard.
Remove from heat and rest for 2 minutes, then serve while the sauce coats the corkscrews loosely.