Use medium-low heat. Slowly melt the butter in a saucepan. Stir often to prevent burning. Clarified butter works best because it has a higher smoke point; it won't burn as easily.

Once the butter is melted, slowly pour in the heavy cream while continuously whisking. This prevents lumps and creates a smooth base. Keep the heat low.

Gradually add the grated Parmesan cheese, a little at a time, while constantly whisking. This slow addition helps the cheese melt evenly without clumping. If it gets too thick, add a tablespoon of cream. If it's too thin, keep whisking over low heat for a minute or two longer.

Low and slow cooking is key. High heat can cause the sauce to separate or become lumpy. Stirring constantly helps maintain a smooth texture.