Mince fresh or roasted garlic. Set this to the side.

Wait for the butter to fully melt and add flour. When the butter fully melts and before it turns brown, add flour and stir vigorously with a wooden spoon. This creates a basic roux. 

Add milk. When the roux is just starting to take a light brown color, while stirring, slowly add the milk.

Keep stirring. Be patient and continue stirring. You are waiting for the sauce to thicken (timing will depend on your stove). After a few minutes of stirring, your sauce will begin to magically thicken (it is hard to miss this). 

Turn heat down to low and add other ingredients. Add in garlic, nutmeg, salt, and fresh cracked black pepper to taste. 

Top your dish with the Alfredo sauce. Add parmesan to finish.