Melt butter: In a saucepan over medium heat, melt butter. Add minced garlic and sauté for 30 seconds until fragrant (do not brown).
Make roux: Stir in flour and cook for 1 minute, whisking constantly.
Add dairy: Slowly whisk in milk and heavy cream. Continue whisking until smooth.
Thicken sauce: Simmer for 3–5 minutes until sauce thickens.
Add cheese & seasoning: Reduce heat to low. Stir in Parmesan cheese, salt, pepper, Italian seasoning, and onion powder until smooth.
Cool slightly: Remove from heat and let cool — sauce will thicken more as it rests.