1️⃣ In a large pot, melt butter over medium heat. Add onions and cook until deeply golden, about 15 minutes.
2️⃣ Add garlic powder, salt, and pepper.
3️⃣ Add dry pasta and broth. Bring to a boil.
4️⃣ Reduce heat and simmer, stirring occasionally, until pasta is tender and liquid is mostly absorbed, about 12–15 minutes.
5️⃣ Stir in mozzarella and Parmesan before serving.