Add the butter and heavy cream to a saucepan. Bring to a very low simmer over medium-low heat and simmer for 2 minutes, stirring frequently.
Whisk in the pressed garlic, salt, and white pepper. Continue to simmer for 1 minute.
Reduce the heat to low. Whisk in the freshly grated Parmesan cheese 1/2 cup at a time, allowing each addition to melt completely before adding the next.
Remove from the heat as soon as the Parmesan is fully melted and the Alfredo sauce is smooth and creamy. Serve immediately.
Notes
Finely grate the Parmesan so it melts smoothly and evenly into the sauce.
Bring the Parmesan to room temperature before adding it to the cream.
Keep the finished Alfredo sauce slightly loose; it will continue to thicken as it cools.
Alfredo sauce is best served fresh. It does not refrigerate or freeze well, so make only the amount you plan to serve.