The Golden Rule: Always turn off the heat before adding cheese or cream.

For perfectly creamy pasta sauce, always remove the pan from the heat before incorporating any dairy, especially cheese, cream, or egg-based mixtures (like for Carbonara). High heat rapidly affects the proteins in dairy, causing them to condense or separate and leaving your sauce lumpy, greasy, or grainy.

The Pro-Chef Method:

1. Remove from Heat: Take the pan completely off the burner.
2. Add Dairy: Introduce the cheese (like freshly grated Parmesan or Pecorino) or cream.
3. Emulsify: Use the residual heat of the sauce and the pasta (and a small splash of reserved pasta water) to melt the dairy. This allows the ingredients to combine evenly and slowly, creating a beautiful, glossy, velvety texture and giving you full control over the final thickness.

Once combined, you can gently warm the sauce back up if needed, but never let it boil. For the creamiest, most stable results, stick to stable options like heavy cream, mascarpone, or freshly grated, high-quality Parmesan (always grate it yourself!).